Lummox

My car seems to be developing an increasingly noisy air con belt / pulley. It's a 98MY UK 2.0 turbo. It slips when cold, and there is a light but constant metallic squealing that sounds like a dead bearing. Could anyone tell me how I can adjust the belt tension, before I look at changing the compressor / pulley. The car had new belts put on at its last service so it might be that it's just a loose belt... here's hoping...

Thanks