Ideally you need a press to remove the old bearing and fit the new one,you can change them using the hammer/BFI method but it is very easy to damage the new bearing or the drum/disc.
If you don't have access to a press,remove the drum/disc assembly,buy a new bearing and take the lot to a local garage who have a press,it will take a matter of minutes to swap the bearings and should be no more than a few beer vouchers for the mechanic doing the job.
