Depends which seals you mean, assuming it is the output shafts for the prop shafts, which it normally is, they are easy. Unbolt the prop shafts at the transfer box end and support or hang them to prevent straining the uj's, take a 6 point socket and undo the nut on the output flange and pull this out. These are usually tight, so only use a six point socket, pull out the oil seal and replace, tap it in evenly and squarely, put a smear of oil around the inner lip and carefully reinsert the output flange taking care not to damage the lip.