I would think you would want to be very careful and only remove the top layer, if not you will have to build up the second either by floating or a build up tile.
Carefully with a box knife, cut a "X" in the middle of the old tile. Go only about the depth of one tile, if you go deeper no problem.
Carefully remove the top layer and peel inward toward the corners and being careful not to encroach on the boundaries of the surrounding tiles. Clean out the area and insert the new tile in its place.
Add mastic if not self sticking and if it is self, then its OK.
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