Removing tiles from plasterboard is often surprisingly more difficult than most homeowners expect. Sometimes, the old tiles stick so well that you can't remove them without damaging the plasterboard. With proper tools and the right balance between force and care, you can minimise the damage to the plasterboard so you don't have to replace it.
Hold a large wood chisel against a tile at the edge of the tiled surface and hammer it gently to force the tile off the wall. Continue to remove all the tiles. The top layer of paper of the plasterboard usually comes off with the tiles and in some areas you might even expose the gypsum layer of the plasterboard.
Remove loose paper and tile adhesive from the plasterboard with a wallpaper scraper.
Mix plaster with water in a bucket according to product label instructions.
Apply plaster to the plasterboard with a trowel, filling any holes in the plasterboard and keeping the surface as even as possible. Let the plaster dry for about one hour.
Apply water to bumpy areas of the plaster with a large paintbrush to flatten them so you have a flat surface for re-tiling.