How to set up a different username one the same PS4

Hello,
Hi I did the upgrade from the PS3 to the PS4. From my User name (Fed Lou) but when i logged into my PS4 it shows my GF user name and cant change it. I was able to log into both of those accounts on the same PS3, using the same PSN ID. Now I still have my GF account to change from PS3 to PS4 but how do i get it into my PS4? do i have to create another user in the PS4? I tried doing that but it tells me to log into the PSN and when i try to do that it tells me "Cant log in into the PSN, another account is using the same ID" (something like that) please if anyone had this problem let me know how to fix it. Any feed back is appreciated.

Thank you in advance.

Fed Lou (Hyperion)