Need help with Lightroom2, space problem.

Basically i've used up way too much space on my computer by saving raw photo files (about 50gigs). What i was wondering is how do i remove the files from my computer (while saving them on an external hard drive) and still retain the ability to edit them in lightroom/photoshop. I really need to get my computer running at a decent speed, it's been ridiculous. Sorry if this doesn't make a ton of sense, kinda tired.