Pc to PS4

Hey, ive just bought a ps4 and a copy of ARR, i played on ps3 a while back but left it, i bought it on pc due to wanting to play again, so i made a new user name and password with the new purchase. When i put the ps4 version on it takes me to the sign in page but will not allow me to use the username i used for the pc, its greyed out with my original username i haven't used for a while. is there anyway to change this or sort this out, i cant find anything to help online :(

If you played PS3 on a old account and then created a new account for PC version then you can't not use the PC account to play PS3 and would need to use your old account that has your PS3 serial if you want to upgrade to PS4 version without buying a new copy.