When submitting an update for your app via developer portal and modifying device compatibility, if the target devices list is greyed out or if the “Edit device Support” link is not present under the "Binary File(s)" tab, please be aware of the following:
When you click the “Save and Add a Binary” button, the devices targeted by the previous binary will be automatically carried over to the new binary and locked from editing. The new binary will support any additional target devices selected, but will not replace the device compatibility of the previous binary. When this happens, under the greyed-out devices you should see the phrase “Targeted by another binary in current or prior version.”
For detailed instructions on how to add/remove device compatibility for an existing binary, please refer to How do I add or remove Device Compatibility to my Live App?