If you have a MacBook Pro 17" Model A1151 or A1212, refer to the first picture. There are four locking tabs along the back edge of the keyboard holding it in place. These tabs must be straightened before you can remove the keyboard.

If you have a MacBook Pro 17" Model A1229, refer to the first picture. There are six locking tabs along the back edge of the keyboard holding it in place. These tabs must be straightened before you can remove the keyboard.