Carefully!
I used to suspend my fiberglass top from the rafters in my garage using ratcheting tie down straps. This allowed me to drop the top down very slowly to get it even all the way around. You cannot be in a hurry while either putting the top on or removing it...
put two 2x4's across the tub. Get someone to help place the top on the rover, supported by the two 2x4's. Hook up the ratchet straps, ratchet the straps up evenly, to remove the 2x4's, then slowly lower the back end down, then finish by lowering the front end.
+1 on DumDum!
The designers of this top should be flogged publicly for a straight week in Northeastern US wet, cold, windy weather on top of a bald hill.