Neil,
Computers have two types of memory (keeping it simple here... so bear with me) --
Hard Disk -- which is where your programs and data get stored. The data on the hard drive is permanent and does not get erased when you turn off the computer.
RAM -- which is where stuff gets copied to, from the Hard drive when the computer needs to access it.
If your computer is reporting that you have a full hard drive, I'd take a look at two things.
1) Buying a new hard drive -- that is the simplest option for the dealer. The problem starts when you want to transfer all your old data and programs to the new drive. Can get messy, unless your dealer finds a way you can do this.
2) Delete stuff you don't need from your notebook.
3) Back stuff that you need but never access, to a removable drive or external hard disk.
If this reply adds to your confusion.. drop these guys a line
onward services
Francis the guy who owns the place is a very decent and capable individual.