Turn off the water supply to the bathroom or to the house, whichever is applicable.
Turn on your Grohe shower mixer tap and allow the residual water to flow and drip out.
Place a towel over the bath drain to ensure no parts fall into the drain.
Grasp the water lines underneath the shelf on which your Grohe shower mixer is seated and disconnect both the hot and cold water lines.
Loosen and remove the brass washers on both stems under the shelf with the wrench, then take the rubber washers off both stems.
Slide the blade of a putty knife between the top of the shelf and the bottom of the Grohe bath shower mixer tap and gently pry it up. If it is stuck in silicone caulk, score and cut the caulk around each line with a utility knife, then lift the Grohe tap off the shelf to finish uninstalling it.