Giant Atx MTB rear wheel quick release not opening
You can use a pipe that you wrap around the QR to have a bigger lever, but be careful not to apply to much force (because you will have a lot more)!
If the lever is stuck against the frame (so you cannot place your fingers around), try with a screwdriver first to pry it open(but put a cloth or something to prevent damage on the frame).

Perhaps the axle of the QR is rusty? -> WD40 then :)