Like its predecessor, the PlayStation 4 will have a user-replacable hard drive. We haven't known exactly how since the system hasn't hit stores, but we've just gotten our first glimpse at the process.
According to German site Computer Bild (via IGN), the hard drive is located underneath a glossy panel on the top of the system. That panel can be removed with a torx screwdriver. It notes that since the system has a 2.5" laptop HDD by default, you could slip in a solid state drive.
It only took them about 21 seconds to swap it out, so all in all it seems pretty easy to do.
This appears to be a dev kit, mind you, so the consumer box might be more difficult. But, the PS3 process was easy enough, so it seems likely Sony would follow suit. The PlayStation 4 is launching with a 500GB hard drive, but as Sony shifts its focus toward digital libraries you may want to consider upgrading eventually.