Locate the position of two studs near where you want to install the niche. Place the niche on the wall between the two studs. Line up the sides of the niche with the grout joints between the tiles. This will make for a cleaner installation and an easier time removing the tiles from the wall. Place a level on top of the niche to check its position and ensure it is straight.
Trace the outline of the niche onto the tile with a grease pencil. Set the niche aside.
Dig out the grout from the perimeter of the area where you want the niche installed. Use a utility knife to scrape out the grout that will be removed from the tiles that will remain to frame the niche. The knife should cut through the grout fairly easily; if it gets harder to work, install a new blade.
Remove the first row of tiles inside the area where the grout has been removed. Use a hammer and chisel to break the tiles off of the backerboard, exposing it. There is no need to remove all the tiles, provided the perimeter is clear up to the tiles that will surround the niche.
Cut the backerboard to remove it. Use a circular saw placed directly next to the tiles that will surround the niche and cut carefully to avoid nicking the tiles. Remove the section of backerboard from the wall.
Test-fit the niche in the cutout on the tile wall to ensure it fits snugly. Remove the niche and set it aside.
Squeeze a bead of silicone adhesive in a serpentine pattern across the backing behind the backerboard and tile in the shower. Place the niche back into the cutout and press it firmly into the silicone.
Squeeze a bead of silicone adhesive around the perimeter of the niche where it meets the backerboard to seal it into place. The niche should be level with the backerboard behind the tiles; when you tile the niche, it will sit level with the surrounding tile. Let the silicone dry completely, then tile the niche.