Delete Game Installs
With few exceptions, a game on the PlayStation 3 installs itself to your hard drive in order to cut down on in-game load times. If you rent a lot of games, this will take up a lot of hard drive space. When you no longer want a game on your PS3, go into your file options and delete that install file. Deleting the installation files of just a few games will free up several gigs (GB) of space on your hard drive.
Don't Hold On To Every PSN Game
When you buy a game on the PlayStation Network, those games are forever tied to your PlayStation Network account. This means if you decide to delete them off your hard drive to clear space, you don't have to worry about paying for them a second time if you want to play it again.
Reformat Your Drive
If you have no problem with starting from scratch, you can always reformat your hard drive. You can find this option hidden away in the "Options" subsection of your XMB bar. This will cause you to lose all data on your hard drive, so be sure you don't want any of the games on it.
Replace the Hard Drive
If you have nothing but essential game files and there is absolutely nothing you want to delete, then it is time to upgrade your hard drive. Unlike other gaming consoles, the PlayStation 3 can have hard drives swapped out, meaning a cheap 40GB PS3 can easily become a 250GB or even 500GB system, so long as you have a laptop hard drive that spins at 5,200 RPM.
Get an External Hard Drive
External hard drives are your best bet if you want to save lots of downloadable content or movies from the PlayStation Store. All you have to do to get the external drive to work is to plug it into one of the PS3's USB ports.