The way your question is worded, all you have to do is remove the seat and safety rails. But if you mean a walkin tub, then that is a different story and we would have to know how it is installed.
Do you have a ready made tub to shower type conversion kit installed right now? Are you looking for a more traditional shower with a glass door and curb? Are you looking for a tiled walk in barrier free shower?
Pictures would help a ton as asked.
Send a couple pictures as well of what you would like the project to look like.