how do i replace driveshaft bearings ?

i went to the garage for a new exhaust and they spent all day trying to fix it on. none of the downpipes were lined up properly they were over to one side so when they fitted it it was knocking against the bottom of the car so they had to bend it to fit. then after i i had spent 4hrs waiting in the waiting i paid for work done . they told me the drive shaft bearings had and were knocking badly . i really cant afford to have this done as the exhaust to be done. so im hoping with a little help from you if you dont mind i will have to try and do it myself
p.s it is a nissan almera r reg
thankyou so much
cheesed off pete