To dissasembly the spraygun, firmly hold its tank, while you rotate clockwise the compression tube(the part which holds the handle) with your right hand.

Unscrew de back lid.

Push out the handle from big tube.

Screw the silicon head holder to make the handle shorter. And assembly the sprayer again.

If you continue with the same problem, then you will have to add washers or some complement to avoid handle touch the piece of rubber. Then, unscrew the silicon head holder.