Hi himmatsj,
 
The installation and uninstallation of a graphics card may vary depending on your motherboard and case. In most cases, you will have to unscrew or unclip the bracket holding the card down. The bracket I am referring to is the metal piece that you can see from the outside of the computer with the video ports coming out of it.
 
Your motherboard may also have a method of ensuring that your graphics card is secure as well. If it has one, you may need to unclip, press down on a clip, or move a lever that secures that card in the socket. Once done, lift the card out of the socket.