I just bought the Quilter's Do-All Hoop for my Designer SE. I cannot figure out the quick release. Do I really have to force it? I am afraid to break it. Please help!

I did have the screw to break on me but the dealer replaced it for free. I too have trouble getting it adjusted but I like it.

You just move the dark grey handle away from the hoop - keeping it flat, don't rotate - to open it, towards the hoop to close - it will then lie flat against the hoop; if not open it ant rotate 180 degrees and close again. Easy peasy once you know how.
Accommodating thicker or thinner fabric: move it in the outward position then rotate - clockwise for thinner fabric, anti clockwise for thicker.