Generaly chains and tensioners are changed at 100k. They are on the left side (drivers) of engine hidden away behind a cover. Not too big a job really, and no you don't need to change everything! Check with the guys on here for advice on what else is a good idea whilst you're there. As for what to look for its actually what to listen for. Set 2000rpm and listen for the rattle. If you can use a screwdricer and hold to your ear and chain cover. You can hear them. There is a link on Premium section to help and a sound bite also. Good luck