That must be a rather old PC, with a 20 Gb disk.
Some PC's come (or a made so later on) with different partitions (drive letters) on the hard disk, consisting - for example - of a 20 Gb c:-drive and a 120 Gb d:-drive the owner forgets about. That's not the best idea, as you will understand. If that's the case, we can tell you how to make the most of that currently empty space.
To clean the c:-drive I'd recommend you download (free) ccleaner and use that to clean a lot of junk. A lot of people here use it without problems.
And it helps (I don't know if ccleaner does that, and it's easy to do it yourself) to turn off system restore and turn it on again. That cleans all old system restore points, that can occupy quite a lot of space. http://support.microsoft.com/kb/310405 tells you how to do it.
But - if you've got a lot of pictures, music, programs, documents on your PC - it might stay rather full even after cleaning most unwanted things. Those, of course, aren't deleted by a program like ccleaner because it can't know what you want to keep and what you don't mind about. Cleaning that is a task that you can only do yourself.
And even after that there might come a time that you'll find it necessary to buy either a second hard disk (adding 100 Gb or so to the 20 you currently have) or a totally new PC.
Hope this helps.
The disk drive on my pc says it has a total of 19.1GB but only 4.69GB is left free. How can I free up some more space, will I have to delete something?
I have Windows XP; I'm not very pc knowledgable when it comes to space, memory, or RAM stuff, so any help given will be truly appreciated.