My product has already been approved but I want to change the price. Before I do this I want to know if I will have to go through another approval process. Thanks!
As long as the price is still within the boundaries you will be fine. For instance: if your product was originally $20 and you raise it above $50, it would need to be re-approved most likely (although this wouldn't take too long).
I'd prefer to create a new product in your dashboard. You can always make the original product inactive. Allows you to play around with split testing etc.