When is the best time to transplant afican violets and how should i do it ? Thank you for your help.

Anytime is ok if need be, but I like to do mine in the spring. To re-pot, tip the pot sideways and gently knock the whole plant out of the pot. Gently loosen off the old soil and pot in the new pot, replace with good draining soil and water it in. Don't feed for a while until you see flowers.
Avs need to be pot-bound to flower, so if you NEED to re-pot, go up just one pot size larger. You most likely won't see any flowers for a while until the roots fill the pot.