Please don't use subject lines like "I need help". What would this forum look like if everyone did that? "Changing Sprites in Flicky" would be much more appropriate in this case.
More importantly, are you looking at the Genesis version of Flicky, or some other version?
I would start by opening up the rom with Tile Molester (or perhaps Tile Molester Mod, or some other tile editor). If the graphics are already there, you can just start editing them; if they're compressed, things will be much more difficult.