Those are probably questions you should take to your artist. There's a lot of questions that need to be answered by you before anyone here could answer yours, and that would be so much easier in person. Where is your tattoo? How big is it? How much space is around it? How much bigger would you be willing to go?
Generally speaking, though, if there's enough room to expand, and you don't mind going a bit bigger, I'm sure your artist could accommodate your request. Not much help, I know, but seriously, go talk to your artist.