Multiple Apple IDs in TestFlight App
Can I use multiple Apple IDs in TestFlight?
If not how can I change my current TestFlight Apple ID to a different Apple ID?
iPad 2, iOS 8.3
Unfortunately no, you can not have multiple accounts for TestFlight. You can change your existing account by going to Settings > iTunes and Appstore > click you account and sign out. Then sign in with your account you wish to use with TestFlight.