I use the Patima G9 housing, and from looking at the pictures of the G11 housing, it appears the lens and fiber optic cable connections function similarly.
To remove a port, simply pull up on the port lock knob at the top of the housing near the lens and rotate the entire lens (I'm not sure if it's clockwise or counterclockwise, because I don't have the housing with me here at the office). Once you rotate the lens, approx. 1/4 turn, you should be able to pull the lens out of the housing.
To install the other lens, simply position the new lens in the same position that you removed the previous lens, push it in, then rotate it in the opposite direction as the one you removed, until the port lock knob snaps into the locking position.
To install the fiber optic cables, simply unscrew (counterclockwise) the cap over the connection point. Then thread the fiber optic cable through, making sure to push it in until it won't go in any further. Then, just screw in (clockwise) the cap over the connection point. It really is a fairly simple system, but it works well, and is easily removable, even underwater.
Hope that helps!