The brakes are Plymouth Acclaim front disc brakes. You can repack the bearings by pumping grease into the grease fitting on each hub until all the water and old grease comes out. Usually 1.5 small grease tubes per hub, makes a mess. 5 rolls paper towels:)
If you want to pull off the caliper, I think there are a couple of bolts or a clip, it slides off. You can find pics in the trailer maintenance docs. If your calipers are seized, don't use auto store ones, get stainless ones from Ameritrail or DHM Trailers.
If you want to pull the rotors off, you have to remove the caliper then remove a big nut in the center of the hub, the rotor will slide off.
I'd repack the bearings, inspect the pads and rotors without removing the calipers, test the trailer brakes, bleed if necessary. Bleed procedure on the maintenance page
I'd also recommend checking the tire clearance on the back of the tires to the wooden trailer bunk board. I've had failed tires from rubbing there on two trailers. The easy fix is to use 5/16" wheel spacers, Mr. Gasket p/n 2371, 15$/pr
http://www.jegs.com/i/Mr.%20Gasket/720/2371/10002/-1?CT=999Hope that helps!
Pete