Open the rom file with Tile Layer Pro, scroll down all the data until you run into the standing/walking sprites and replace those two with each other. If you're just going to play it yourself and not sharing the hack, I guess you don't have to worry about not having a right bicycle sprite. If you want to do something about the bicycle sprite as well, you're going to have to "re-write" it with Tile Layer Pro there.
Thank you very much! I really do appreciate this. I spent a lot of time yesterday trying to find out how to swap the sprites, but had no luck until now. Thanks again!