I just took mine off and put back on. The bottom brackets should be mounted pretty much flush with the front of the tree and almost straight out. Snug these down and hold the shield up to them to make sure they are right. If ok, tighten and recheck.
The top arms need to be installed and not made tight. You can approximate by measuring the straight distance between holes in the shield and put arms that distance apart. You also need to measure back from each arm to the handlebar to make sure they are straight. Adjust with them fairly snug holding the shield up until it looks like it will fit right on, snug the arms a little tighter (not final yet) and recheck. If still good, tighten them and install the screen with the 4 screws.
I've found this much easier than trying to tighten the arms with the screen on.
