Guitar strings

I picked up a used guitar recently. The strings are probably a couple of years old. Should I change them? How do I know when they should be changed? I noticed I comes out of tune now and then. Would that be an indication I need new ones?

 

Going out of tune could be a matter of old tuners . Sometimes they have a screw that can be tightened .
If not - then we just tune a fish .

 

Hey tikoo, thanks for that. I didn't think of the screws. I just realised that this category is for musicians, which I don't consider myself. I'm more of a novice and not in any band. A musician would certainly have thought right away about the screws!

 

Two year old strings are well past their prime.

That's probably not the tuning problem though...

 

The most important screw - it tightens or loosens the cogged wheel that drives the spindle
which winds the string unto tension .

 

Is it an Acoustic or Electric Guitar ?
Get locking tuners, that way the string will not shift if they or are new .