There are some guides on them, for example
HERE is one... but they are really geared towards devs vs end-users.
I'm not sure how experienced you are but if you need TestKit Firmware I can link you to that, although if you are like me and more of an end-user than a dev then you probably could sell it for a decent price and get a retail PS4 console.
If you want to sell it we have a
Buy, Sell and Trade section you can list it in, and it may even go to another developer here who could put it to some good use for the scene.