if the belt doesnt cure it then its a pulley. they are only held on with a single centre bolt so easy job to change at home. if its the tensioner thats the problem then thats held on with a few bolts but still easy job to do.

only extra thing i can think you might encounter is a lower plastic cover but thats a few 10mm iirc bolts and its off, easy peasy.

just follow the haynes. the hardest bit is slackening off the tensioner. think its a 13mm spanner on the centre bolt and you pull one way, you'll see, but the spring is bloody strong so either use a long spanner or a socket on a long bar for added leaverage.