Mitch wrote an answer about Black Diamond Axis 33 Backpack - 1892-2136cu in on August 19, 2012
There are two things you can remove, the band itself, or the band and then the back pad (the padded thing that is connected via a swivel to the bag itself).
For the strap, after you untie all the straps that tie it to the bag, there are a few velcros that keep everything tidy. First, along the back strap, you'll notice sleeves on either side, through which the thinner strap goes through (the one you'd use to tie around you). Pull this latter strap out - there is velcro inside the sleeves you'll need to deal with. Then, the way the back strap goes through the back pad has a similar design (velcro). Once you deal with that velcro (push your hand through), you can pull the back strap through.
This leaves you with the back pad still attached to the bag. To get this one out, you'll need a second pair of hands and a screw driver with a hex head (or, better yet, a crank handle screw driver). Ask your buddy to pull back slightly the upper lip of the back pad - thus exposing the connection and the screw. Unscrew it.
This also allows you to pull out the back piece (plastic + metal frame), leaving you with the textile bag alone. It's probably unusable as-is since it has that hole in the back (where the pad was), but much easier to wash.