Upgrading to the digital version of Assassin’s Creed IV: Black Flag, Call of Duty: Ghosts, Watch Dogs or Battlefield 4 on PS4? Then you'll need to remember not to sell the PS3 version.
Sony has revealed that each of the above games on PS3 come with a single use code that can be entered on the PlayStation store for a discounted PS4 version, however for this digital PS4 edition to work the original PS3 disc must be in the drive.
Even though the PS3 versions do not actually work in the PS4, we're guessing that Sony has implemented some code within the disc to allow this to work and therefore combat a huge amount of second hand games from flooding the market.
Check here for detailed instructions on how the upgrade from PS3 disc to PS4 digital will work. There is currently no mention of other titles being upgradable such as FIFA 14.