Removing ceramic tiles from plasterboard walls requires more finesse than taking them up from floors, because with floors you can just break the tiles up with a sledgehammer and remove the pieces. Walls are more fragile than floors, so you need to be more careful about it. If you can get one tile out, it will allow you to get underneath the others with your mortar chisel and knock them out without knocking a hole in the wall. Ceramic shatters like glass when dropped, so make sure to protect your floor and yourself.
Lay a canvas tarp at the base of the wall. Fold it over a few times, to provide extra protection to the floor from falling tile.
Use your grout saw to dig out the grout around one tile, scraping the blade forward and back and breaking up the grout. Remove the grout all along the four sides of the tile.
Press the tip of your mortar chisel in one of the open gaps by the tile. Hold the chisel at a narrow angle to the wall, so you’re pressing the mortar under the tile rather than under the wall. Tap at the chisel with the hammer, moving the chisel along the length of the tile until the tile breaks out.
Use the open space created by the extracted tile to set the chisel against the base of the next tile, against tapping at the mortar under it.
Repeat and continue, chiselling out the tiles one by one. Try to keep them in one piece if possible. Always chisel at the tile, not the wall.
Scrape the wall with your paint scraper once all the tile is out to get rid of any residual mortar and grout. The wall is now ready for re-tiling.
Wear eye protection when removing the tiles.