Changing the strings on a guitar is probably the most basic form of maintenance for your instrument. It is something that you will do fairly often. Some guitarists can keep the same set on their guitar for months, others change within a few weeks or less. A couple of signs that strings need changing might be that they feel a bit rough or sound dull. The unavoidable reason for changing a string is if it snaps, which can be the most frustrating!
There is no method of changing your strings that is set in stone, people often find a way that works best for them. The method as follows tends to be one that many find to be the most stable and is fairly quick!
Be careful around the ends of strings, they can pierce skin and while a puncture from a string isn't too painful, they can bleed a lot. Also take care not to over-tighten when restringing, when first putting strings on it's fine to keep just enough tension to hold it in place until you tune up, if you tighten too much the string could snap which could catch you and hurt, and also would mean you need to replace the string again.
I'd recommend getting your teacher or a music shop to replace strings at first. When you do want to start, ideally the best practice for changing strings is if one snaps and you try replacing just that one, that way if it goes wrong it's just a matter of getting one replaced and not all six.
You need a set of new strings (or a single string if you only need one changing) and something to snip the ends off the strings. If you have nothing to hand you can make the ends of strings into a tight loop. Countless guitarists including myself have changed strings with the guitar on their lap or in the back of a car on the way to a show, it's not the ideal position! Laying the guitar on a flat surface with something to rest the neck on is probably considered the best way.
The first step, is to remove the old strings by de-tuning each one until loose enough to unwrap from the tuner. Then remove the string from the bridge, as detailed below, different guitars have different styles of bridge so they aren't all quite the same.
It is recommended to change strings one by one to keep the tension even along the whole guitar. Removing all strings at once also makes cleaning the guitar much easier, the worst places for dust are under the strings.
When ready, take your new strings out of the packaging, make note of which string is which. Some string manufacturers have colour coded ends which makes it much easier to tell which string is which, but others don't, so pay attention to avoid putting the strings in the wrong places.
Place the string through the bridge, bring it up the neck, into the nut and through the tuner hole. Take the excess string and pull it tight towards the closest edge of the headstock. Bring the string around the tuning peg and under where it meets the hole in the tuner then pull it back over the top of this section of string. Tighten the tuner clockwise until there is good tension. Bare in mind that it doesn't need to be close to in tune yet, just tight enough to hold the string in place.
Repeat this for other strings, making sure they're all in the correct nut slot and going to the correct tuner. If the string gets put into the wrong nut slot then that's not a big deal, just loosen it and put it in the right one. If you string it up to the wrong tuner however, it means a bit of extra work removing it from the wrong one and putting it in the right one!
Next, tune the guitar up. New strings will go out of tune easily as they are not stretched out. To help with this pull the string away from the guitar in various places across the neck then tune back up to help speed up the breaking in process.
Re-Stringing an Electric Guitar
An electric guitar usually requires the string to be put through a hole in the bridge, which is located on top of the guitar for some bridges. Alternatively, the string is fed through a hole on the back of the guitar for others. There are bridges which are more complex but generally you won't come across these when you are first learning to re-string.
Re-Stringing an Acoustic Guitar
Acoustic guitars sometimes have a bridge which only requires putting the string through like on some electric guitars, but most of them use bridge pins which hold the end of the string in place. With these, remove the bridge pin, put the string in, replace the bridge pin and pull the string while holding the bridge pin down until it feels locked in place. When removing strings most bridge pins are fairly easy to just pull out, sometimes a bridge pin removal tool may be required. Don't use pliers, this can cause damage to the bridge pin and if you slip it can cause damage to the guitar.
Re-Stringing a Nylon Guitar
Nylon stringed guitars are slightly harder to change. They don't have ball-ends, so to attach at the bridge it requires a bit of a wrap-around knot. Feed a few inches of string through the bridge, then loop it back round under where the string meets the bridge, the end of the string is then tucked under the section of string which has been wrapped over the top of the bridge. Pull this tight. At the tuner it needs to be wound enough to trap the end under the tension of the string, but other than this it is a similar process.
Well done! You've re-strung your guitar!
These steps should be all that's needed to change strings on any standard guitar. Make sure the strings are fully through the bridge. They get caught and slip while tuning up, this doesn't cause any damage but it does make the whole process take slightly longer!
Once you do get comfortable changing strings it feels like quite a simple task and can save you a lot of money. Although, I don't think the fear of having a string snap on you while re-stringing ever disappears!