I'm trying to delete the files on the CD but it keeps telling me that its readonly and cannot be deleted, im using the default windows explorer

Deleting files of a non-RW CD/DVD(etc.) is like dividing by 0...

I work tech support; I'll handle this!

Sir, you most likely will not be able to delete any files from the disc unless it was specifically formatted to allow you to do so.  If it's a DVD movie designed to be played in your DVD player, you will certainly NOT be able to do so.  If you know for sure that it was formatted to allow you to delete files, unless you see the letters "-RW" on the disc, deleting files from the disc will not result in any more space being available on the disc.  If you see the letters "-RW" on the disc and it wasn't formatted so that you can delete files, you'll have to ERASE THE ENTIRE DISC to remove any files from it.  If you simply want to destroy the contents of the disc, you'll need to destroy the disc itself.

As to what you're trying to accomplish, your best bet will be to either pony up a few bucks for a blank disc or check the Ubuntu forums as to how to install directly from an ISO image.