I have been purchasing and downloading games on my ps4 for a while. Now my memory is getting pretty full so I can no longer add to my library. What would be ideal is if I can get a hard copy of all my downloaded games, but I don't want to pay the full price again.
Is there a way to trade it for the disk version, or has anyone heard of a way round?
No, there's no way to do that.
But you can safely delete games from your PS4 and re-download them at a later time. Digitally purchased games are associated with your profile and you still "own" it even if you don't have it installed. This can make room for more digital games.
Also note that even if you have a disc copy of a game, it has to "install" to the PS4, which functionally is the same as having the digital copy with the added hassle of needing the disc in the system to play. Essentially, there is no advantage at all to having a disc copy unless you like collecting physical objects for their own sake.
As mentioned, you can't get a disc version of a downloaded game for free. However, in addition to StrixVaria's suggestion of simply deleting the game, you can install a larger hard drive for your PS4 as Sony has made it very easy to swap hard discs(you backup your current hard drive to an external drive, swap drives and then restore from the backup). If you have upgraded to the latest firmware, you can also simply attach an external drive and offload games to there as mentioned in pew's comment.
