Do you have SET20 tapered roller bearings with the external seals, hence the question about bearing removal? If so, I cold chisel the retainer collar, then press off the bearings...trying to do both at the same time with the press requires scary high force and increases the wear on the axles where the bearings and retainers seat.
If you've got the sealed ball bearings with the separate internal axle seals, then there's no need to remove the bearings to swap the seals, but I'm sure you know that. If you have the aftermarket sealed ball bearings with the o-ring in the outer race intended to be run without internal seals, then same method as the SET20's, just different parts.