I was approached by my cousin recently to play the guitar for her coming wedding in a few months' time. Well, as part of my wishes to her for a blissful marriage, i agreed to play a few songs on her coming big day. All my family members including relatives know that i used to be an avid guitar player (especially during my schooldays). I have not actually played my guitar for quite some time already, so for now to practice for my coming cousin's wedding, i made my way down to Peninsula Plaza not long ago to buy new strings for my guitar.
Strings require changing for many reasons. They break due to being over-tensioned, or they have become rusty and lose elasticity so they can't stretch. They can also be broken by heavy handed playing, or sharp edges on bridge saddles or tuning pegs. Strings also lose their tone and brightness over time making them sound out of tune the further up the neck you play and no amount of tuning will get them back in tune.
When i used to play my classical guitar a lot in the past, I changed the strings at least every two weeks (more than that if I'm using it for gigs). It's probably not necessary for beginners to be quite as diligent with keeping new strings on their guitar, but changing strings a minimum of every couple months is a very good idea.
It is a fact that if you own a guitar, you will need to change guitar strings at some point. Just like brake pads on a car, guitar strings wear out with use. Old guitar strings often behave badly, they'll lose tuning more quickly, sound less "bright" and give you problems with intonation.
Changing strings is relatively easy and strings are quite cheap so if you are changing them for the first time, get a couple of sets just in case you make a mistake, like accidentally putting a kink into one. It would be very difficult to cause any major damage to a guitar by re-stringing. The worst you are likely to do is break a couple of your new strings while you try to fit them by perhaps tuning them to high.
Being able to change guitar strings is one of the basic maintenance tasks that any guitarist will master, along with tuning the instrument.
As a personal note, I prefer my strings to be played in, not just so bright and zingy as new strings, but with the intonation still intact and still capable stretching for string bends without feeling that the next bend is going to snap it. :-)