World-of-warcraft – WoW Tailoring Bags in MoP

When replacing bags, it works best if the bag you want to replace is completely empty -- then it's simply a matter of dragging the new bag to the place on your inventory pane. The equipped bag and the newly bought bag should switch spaces.

I believe you can also simply drag the old bag into a bank bag slot, leaving the space in your inventory empty, after which you can simply drag the new bag into the empty space.

Personally I prefer Altoholic. You can see and search bags, banks and guild banks across all you characters, but also Altoholic does so many amazing things for multiple characters as well.

For each character you can also see what currencies, bag slots remaining, gear they have, their talent build, if they have mail and how long until it expires, what recipes they have, their reputations... With 10 alts, I couldn't live without it at this point.