I got so carried away downloading files that I have managed to use all my memory and now it won't even allow me to delete any files to free up the memory.
Reboot the computer. Part of your hard drive is eaten away by VM shortly after a reboot; restarting the computer should give you a gig or two to work with. From there, you can get to deleting things.
It's not memory that is full, it is the hard drive.
#0 - Reboot
#1 - Empty the Trash
#2 - If you have any obvious files of your own you can delete, do that and empty trash.
#3 - Open your web browser(s) and delete their caches or 'temporary internet files'
#4 - Go to www.versiontracker.com and download DeLocalizer. Run it and delete un-needed language resources. That should gain you another GB or so.
Now -- get yourself an external drive and move your bunches of {whatever} to the external. Take the opportunity to install an OS on the external drive and some utilities, so you can boot from the external if you have trouble with your internal.