You will be wanting to be very competent to change the bearings in a Bosch!
You will have to remove everything connected to the drum unit in the machine, lift the entire drum out the machine, split the outer drum in half, remove the pully from the back and pull the inner drum out, then you really need the proper bearing puller to remove the existing bearings (at a push you can drive them carefully out using a hammer and a large metal punch).
you then use the bearing puller the other way round to fit the new bearings back in (again can be done with a hammer and a punch, but be very careful to drive them in level!), refit the oil seals, refit the inner drum and screw pulley back on, reassemble the outer drum, fit back into machine and reconnect everything up again.
You would be looking at a 3-4 hour job that really requires two people if you know what you are doing, if you don't know what your doing to start with it's not a job a would suggest anyone tackles themselves! if you do decide to do it put aside a whole day and get somebody to help you with the heavy parts!