Luisa48, According to your manual, as you look at the adjusting lugs, it is the top left. Using two 9/16" wrenches, hold the inner and loosen the outer nut. Tighten the inner nut to raise the top. Use caution to prevent raising it TOO much. It may take quite a few turns to raise it, I start with about 3 full turns, raise the top to see where you are and re-adjust as necessary.
Treeclimber