Cabin filter replacement for the 2007+ S80 is not a difficult task, For the first time it should take 15 minutes
after that it should be a 5 minute job. Start with removing the long side cover trim piece of the center console.
its connected with push clips so pull firmly to remove. then the black cover with light under the glove box. It takes a  torx driver .
do not remove the glove box!!!look at the way the clips slide the cover out from the firewall.
Use a  piece of masking tape to mark the cabin filter cover  with an up arrow before you remove it ....
you will see why later, as the cover looks like it can go back on all kinds of ways and none work except the correct orientation.
the filter will pull out and you will have to replace it in the same manner it comes out
 it might need to be flexed a little with some persuasion
I replaced my cabin filter with the charcoal factory filter Volvo sells
 of course reverse the instructions for reinstalling the filter