Sure it’s simple to change the price—I assume you mean gig extras since as far as I know they all are a basic $5 unless you are using the packages. (I have seen a few that are more though.) Click on the word EDIT in the upper right of your gig. Go to the second tab on the top, click on it and put whatever price you want.
I’ve never tried to change the category of a gig. It’s possible customer support would do it for you but I’m not sure. You can ask them. If you don’t have any reviews you could just make the gig in the category you want, then delete the other one.