You can buy caps that will allow you easily grease your bearings in minutes without taking the wheel off. Costs about 20 bucks are so for a two piece set. Hook a grease gun up to the cap zerk and squirt new grease in. Doesn't get easier than that. As far a replacing bearings, I agree with Zilla. A way to check to see if bearings need replacing is the grab the top of the wheel and push and pull on the tire. If it pops or you fill it "wiggle" a bit, it is time to replace those bearings. But before you jump the gun and pull the wheel to replace, check the axle nut for snuggnish. It could very well have backed off a bit and the hub is loose. This may or may not sound complicated to some, but it is really easy stuff on these trailers. It can get a bit more complicated on tandems, electric breaks, and huge trailers like the Renegade to do this types of inspections. On the big boys, best to pull the wheels off and give a physical/visual inspection.