Removing Video Card

Hi I recently got a free computer from a friend and I want to replace the old yucky vid card for a newer video card in it. There is this plastic clip/bracket thing. how do i remove it or arrange it so i can get the old video card out? just wont budge. im more used to screws instead of this bracket thing -_- here are some pictures. it is just stock pictures
http://img502.imageshack.us/img502/6350/vidcard1gp4.png
http://img175.imageshack.us/my.php?image=vidcard2sx9.png