Display won't come off.

I want to replace my rear camera and lens so i tried to open up the iPhone. However the screen won't come off completely. It remains stuck in the top right corner. I tried prying it open and sliding a credit card inbetween the frame and the display, but it wont open up on that particular area. I can feel that if I pull on the suction cup even harder it might break. What am I doing wrong?