I'm sorry?? I realy don't know what you are talking about.
You have the CA SA58 quad front rail that has 4 rails. One top rail, one bottom rail, one rail on the left and one on the right.
Uninstalled
Installed:
To detach the front rail you must. Unscrew 6 screws which you can see from the top. If those 6 screws are out you can lift up the top piece of the front rail handguard.
To detach the bottom part you have to unscrew one screw which you can find at the front of the bottom rail near your front sight.