How to replace serp belt in 2007 Suburban?
 

I apologize if this has already been answered but I couldn't find it searching.

I'm trying to replace both the A/C and serpentine belt in my 2007 Suburban. The A/C belt is easy as I can rotate the tensioner to loosen it.

However, I can't seem to find out how to lessen the tension on the main serp belt. I've tried rotating the idler pulley bolt both ways but that has no effect.

Thanks in advance.