Pop the rubbers off the end and you should see the ball ring/sleeve of the coupler. The sleeve/barrell will just thread out. There's a tool to loosen them but it's nothing a good pin punch won't do if you're carefull. I don't remember now if you need to remove the lever and it's shaft firs or the barrell will come out anyway... but you need to remove the lever at some point. Then you're left with the bare aluminum housing. All coupler kits now available for the Rexroth valves are leverless. They provide a kit with the new coupler barrells and covers to go over the holes where the levers used to be... but I never had any luck keeping them in place. Just renew the seals in the body and thread the new couplers in. Done.
As Bern said... they do leak a bit at times but that's typical of most quick couplers.