Noramlly you use an antifungal for ringworm, treatment time varies. Sometimes up to 3 weeks.
IF you get another guinea pig make sure you quarantine it in another part of your house behind a closed door for 3-4 weeks. When handling the new pig use a certain shirt for that time and change before you go to your own herd. Also on that note make sure you wash your hands thoroughly before handling your herd.
Ringworm is contagious so watch yourselves also and anyone else that may have handled them.