Very gently remove the rubber seals by prising out the seal from the inner lip. You can use a penknife or small screwdriver but do not push it too far into the bearing or you may damage the retainer (cage).
Use a degreaser and some paper cloth to make sure you fully clean away all old grease before relubricating. Alternatively, you may use a can of spray degreaser with a fine straw applicator to direct a jet of degreaser into the bearing assembly. It may take a few applications, but make sure to get all the old grease out.
Once satisfied that the bearing is completely grease-free, use a lint-free cloth to dry the bearing. At this point, take the time to inspect the bearing and decide if it needs replacing. Make sure the bearing surfaces are completely clean and oil free before adding new grease.