Start with feet hip width apart in front of your body and the ball between your mid to lower back and the wall
Raise your arms in front of you for balance and keep your back straight at all times
Slowly lower your body and roll the ball down the wall until your thighs are parallel with the floor
Now slowly return to the starting position and repeat until you can no longer maintain correct technique
Tips
Once you have lowered yourself for the first time, be sure that your knees are not protruding over the line of your toes, if they are move your feet forward