if by popped you mean broke, snapped, etc you just go out and buy a new pack of strings. if theyve been on it for a while change them all but if theyre not too old like 2-4 weeks (reallydepends on preference) just change the one. and if you need instructions to change the string just google it or
www.ultimate-guitar.com has lots of lessons n stuff of tha tnature.