dumb basic gamertag question..

how would one go about changing a gamertag from one of my oG's to my main account?

 

All that you do is change the gamertag on your "oG" account by clicking the middle guide button,profile,edit profile, then gamertag.

Change the gamertag to something else (this will cost 800 msp).

Now go to the same place on your "main" account and change the gamertag (another 800 msp) to the "oG"

Be sure to do this quickly because once you change the "oG" account's gamertag, then it becomes available to everyone until you change your "main" to it.