Go to account.microsoft.com and sign in with your Xbox account
Select Your info
Choose Manage how you sign in to Microsoft
Add a new email address or phone number if needed
Verify the new email address with the code sent to it
Set the new email as the primary alias
Remove the old email alias if you want it no longer linked to the account
Sign out and sign back in on your Xbox with the updated email
If you cannot change the alias, contact Microsoft Support