I think this chassis has the driveshaft-mounted parking brake, so do one end at a time and block the wheels on the end you leave on the ground so it can't roll. You'll need a block, or just use an old brake pad, to push both pistons in the dual-piston caliper back at once. Change any flex hoses. Our E450 has one to all four wheels. Shouldn't be a bad job is you can handle the wheel removal and the torque on the lug nuts. Rear disk brakes are a whole lot easier than rear drums integrated with the hubs. Drive axles had to come out and wheel bearings dismantled.