It's simply a case of removing the wheels, prising the dust / grease cap off the centre of the brake disc or drum. Beneath this you will see a split pin through the stub axle, remove this with a flat screwdriver or long nose pliers so that you can get access to the retaining nut.
Unscrew this nut and remove the disc or drum, the bearings will come out with it.
Clean the bearings on either side with petrol or similar and allow to fully dry before regreasing them.
Reverse this process to refit making sure to only tighten the retaining nut as far as it will go by hand and not by socket just enough to remove any play.
Insert a new or straightened split pin and repack the dust cap with fresh grease and use a rubber mallet to reinstall. Bingo you should be sorted.
