Unfortunately, Flash Pro doesn't have an editable setting pointing to the AIR SDK it uses, so you need to duck into its folders and overwrite the SDK it came with. Inside your Flash CS5 install directory there should be a folder called AIR2.6
. You want to back that up somewhere, and put the new SDK in the same place (with the folder name AIR2.6), and Flash will start using the new SDK.
The other thing you'll want to do is to put an updated airglobal.swc
in your install folders so that you get AIR3.1 code hinting. See the instructions on this page - those describe how to update the IDE to target Flash 11, but the process is similar for AIR except that you update airglobal.swc instead of playerglobal.swc. You can also make some new AIR3 publish profiles, similarly following the instructions on that page for Flash 11.
It's a little tedious but unless somebody makes an .mxp to update for AIR I'm not sure there's an easier way. Good luck!