Worth doing the glove test, but on your car if it hasn't been done before it's almost certainly due. Not too hard, but as above, fiddly but OK if you have a decent set of tools.
There's a "how to" in the Articles section at the top of the forum, here:
https://www.volvoforums.org.uk/showthread.php?t=46946
Unfortunately no photos due to Photobucket's greed and idiocy, but the words alone should help.
When I did mine I got a complete kit of parts from FRF at a reasonable price - great service and they will post. For details see the dealer section.
Go for it!
There's a "how to" in the articles section on replacing the cam belt too - again, a fairly easy job relative to many other cars.