I think it's relatively straightforward once you've decided which drive you want - that process is highly dependent upon how much you want to spend though. SSD's are still relatively expensive and I can't imagine you'd want less than the stock half GB. You might be interested in the hybrid SSHD that is much cheaper and still gives a bit of improvement but obviously not the full effect.
Personally, I get a little nervous messing around in the guts of things without watching a ton of videos first.

I'm
almost certain the process doesn't void your warranty but I'd still suggest the following:
or
There is also a great long discussion about particular drives and people's experience here:
http://www.neogaf.com/forum/showthread.php?t=716288
Eurogamer talks a bit about it here:
http://www.eurogamer.net/articles/di...our-ps4-to-2tb
Eurogamer also give some nice breakdowns of the Bloodborne loading times under various hard drives in the article that EE mentioned but didn't list. At least that is the article I think he mentions . . . I can't seem to line up his numbers.
And finally Sony has their official post about the process here:
https://support.us.playstation.com/a...pgrade-ps4-hdd
I hope that helps a little (take your time with it, don't rush like I tend to when I get nervous.) Good luck sir!