There's no legal way yet, but Sony might be coming out with something. If you can't wait for that and want, there's a bunch of homebrew things which are... well... the name pretty much explains it. I found a bunch of sites through google, which have instructions, and even forums where you can nag on the members for assistance. But the trade-off is you can't play current games which require the latest version of firmware, because with each update they're updating their security. Currently version 2.7 is out.
I never really got into homebrew, it was too complicated. Needed two memory sticks, there were certain specific ways to install it, blah blah blah.