Removing the shower walls---First peal off the top row of tiles using a heavy bent scraper.
Next peal off the two outside rows.
Install a blade in your Sawsall-Upside down -so you can make a shallow skim cut along the edges of the tile. Be careful not to cut any deeper than the thickness of the board.
Now get a hammer and punch a couple of hand holds and pull--that's about it--
Removing the floor is a hammer and pry bar job,
Shower pan removal--If you can get at the drain from below--cut off the old drain and then just lift out the old pan.
If every thing must be done from above---I use a Skill Saw and make several plunge cuts around the drain--once the pan is separated from the piece that has the drain--
Remove the pan--saw off the drain with a long Saws All blade.
Replace the P-trap and follow the directions that come with your new drain set.
Rather over simplified instructions--You have to figure out some things as you go.---Mike---