OK Lowe...Mine on the left looks like this...
Now if you look under you might see a bracket like this on the left (has the holes in it)
If you move this out of the way (just slide it - it should move but be under tension).. then pull down the screen say 2ft... then look up with a torch from behind the screen, you should JUST be able to see a yellow screw like below..
Other screw was not visible from where i was standing (but as thats the upper limit screw you should not need that really?)
Now you have to FULLY extend the screen until it stops.. THEN you can put a screwdiver in and turn that yellow screw clockwise... I had quite far to go so did loads of turns.... Then you raise the screen back up and then down again till it stops... it should now be less than it was...
I carried on till i got it close... but now i can fine tune it on my own without the wifes help to hold it!
If you go to far up, when you turn the screw the other way, the screen should drop as you turn it...
Hope that helps...
Ignore comment below - its for google searches that may help others..
platinum147 platinum home cinema screen adjust lower limits