How was the ringworm diagnosed? Other skin conditions may look very similar but require different treatment.
If it is in fact ringworm, and the lesions are small and haven't spread past the head, you can use a topical anti-fungal like micatin, tinactin, or other athlete's foot treatments. You cannot use it close to the eyes or in an area the cat can reach to lick it off; in that case you should consult with your vet about systemic treatments such as oral itraconazole.
Cultures are needed to diagnose as well as to monitor progress. It can take many weeks to get rid of it.