To replace the rear shields is a beefy process:
Calipers off (easy)
Caliper carriers off (an utter ball ache)
Discs off (easy)
Hubs off (You need a massive breaker bar and high quality triple square socket for this job, otherwise, utter ball ache)
The hub bolts are one time use, so budget for replacements.
I would only tackle this job when the rear pads/discs need replacing as it's not a 5 minute thing by any means.
You can apparently fit new shields without removing the hubs if you trim a section of them away with tin snips....but that's just a bodge.
A lot of people are tempted to bin them off, but I would advise keeping them. They protect the bushes and dampers from the heat and nasty brake dust, not to mention all the road detritus that can flick up into the brakes and wedge in there, causing more unnecessary damage.