Hi,

I’ve got this info from the APA (Aust Physiotherapy Assc.) brochure, calf stretch exercise to relieve leg cramps:
Stand with both hands against a wall. Place one leg back with your knee straight, heel flat on the floor and toes pointed straight ahead. Slowly lean forward, bending the front knee. Hold and feel the stretch in your calf muscle. Repeat for the other leg.

Hope this helps!