Really not that complicated of a process, this was a pretty good guide:PS4 question.
How do I go about increasing the storsge capacity? Bit of a pain having to delete a game everytime I have a new one. Theres hardly anything on there in the first place, only about 3/4 games.
https://www.ign.com/wikis/playstation-4/How_to_Upgrade_or_Replace_Your_PS4_and_PS4_Pro_Hard_Drive
disclaimer: I did this a while back, not sure if anything's changed since