What BC_Programmer said.
Nothing short of actually removing a large portion of what you have on that drive is going to free up disk space.
It's the same principle as cleaning up a compulsive hoarder's house. Just wiping off the counters is not going to clean up the mess--the hoarder needs to get rid of some of his/her junk! (either that or get a storage unit, but they'll just fill that up as well...)