Fill the spray bottle with a 50/50 solution of vinegar and warm water. Shake the bottle gently to mix the vinegar and water. Spray the solution onto the showerhead, concentrating the solution in the crevices. The vinegar/water solution will help to soften mineral buildup so that you can remove the front of the showerhead with less force. Allow the solution to sit in the showerhead's creases for 10 minutes.
Cover the showerhead with a terry cloth towel. The towel will protect the showerhead's finish from scratches as you use the wrench. A hand towel is easier to use than a bath towel, but either type will work.
Adjust the wrench so that its width is just large enough to fit over the showerhead with the towel on top of it. Once you have slid the wrench over the showerhead, tighten it until you can't tighten anymore.
Turn the wrench counterclockwise. If you feel the towel slipping on the showerhead, spray it with the vinegar/water solution to give it more grip. Turn the wrench until you feel the front of the showerhead loosen. Remove the wrench and the towel, and remove the showerhead with your hand.
Replace the front of the showerhead after you have finished your maintenance inside. Hand-tighten the front of the shower head instead of using the wrench so that you'll be able to take it off easier next time you need to clean the inside or adjust the flow restrictor.