I have tiled my shower and one tile didn't stay so I am trying to get the dried thin set morter off so that I can replace the tile what is the best way to do this so that I don't knock off the rest.

Use 1'' stiff putty knife. Start at edge of installed tile and work toward center. Take your time.

Chuck

Multimaster oscillating tool with rasp or it's equlivents. See Harbor Freight Tools (http://www.harborfreight.com).