It depends on you and the type of tub and if you have tile walls.You might be able to remove all and just slide in a new shower unit but dont count on it. You well have to redo your water lines and may have to build a base for the shower base unit to sit on for the drain again it depends on where the old tub is sitting and if you are on a slab or wood floor. Second floor, first floor.
First time diy I would get help from a friend who has done this type of job before. You might get a plumber to do the pipes and you do the rest.
I know where you are coming from the price to have this work done would not be cheap but unless you have done this kind of work before I would take a step back and give it some thought.