Yes, first of all you need to waterproof behind that wall. Tile just applied to drywall in a tub area isn't designed to be waterproof.

Although this is directed towards a shower only, this does show the proper layers on top of the raw studs. Don't forget the insulation in the cavity.

If it's been previously splashed by any tub bathing, I'm betting that you will find mush behind the wall. Also, not every tub is designed to serve as both tub and shower. It will need an integral tile flange to serve as a tub/shower.

The little turned up lip is the tile flange, and your tub needs to have one to serve as a tub/shower. If it doesn't have it, replace it. Tubs are really cheap.

Removing tile is very easy. 30 minutes with a hammer and a Wonderbar should make short work of it. The harder part is putting tile back in, up as high as needed for a shower, including the most important part: waterproofing. It's not rocket science, but it is important to do it right, as live wire oak has outlined.

You basically need to pull out the drywall, put up cement board, paint Red Guard over top of it, then tile on top of that. Alternatively to Red Guard, you can put plastic behind the cement board as the barrier. Just don't do both or you'll create a moisture sandwich.

Thank you very much. It's so tempting to do a half-way job but I know I will regret it. I know my wall is sound because I'm the only one using this bathroom and don't splash much. Will wait until I'm motivated to to it right!
Thank you again.