how do I get to sudo apt get clean?

To get such a command you have to open the terminal:
Applications - accessories (or something like this) - Terminal

But if the system says you're out of space... this order may not be enough. You should really delete some big files like Videos or so...

Greetings

Open a Terminal (Applications - Accesories - Terminal) and run (copy&paste + Enter)....
sudo apt-get autoclean
sudo apt-get autoremove
sudo apt-get clean
With this you will remove all files in /var/cache/apt/archives/

I really would recommend you to install Bleachbit for deeper cleanning tasks (thumbnails, etc). To install it:

sudo aptitude install bleachbit

You will find it in Applications - System Tools - Bleachbit

If you prefer to do it with the commandline, you can clean ...
TRASH - Recycle bin
 rm -rf /home/*/.local/share/Trash/*/*
 rm -rf /home/.Trash-0/*/*
THUMBNAILS (probably you will earn a lot of space)
        rm -rf /home/*/.thumbnails/*/*
OLD KERNELS (do it with Synaptic best and leave the last 2 of them)

Hope that helps

I think the initial problems came on install when I migrate stuff from windows.I did a reinstall whitout it, then everything worked fine.I'm a little green with this system to say the least.But thanks to midnight and Pablito, I have more stuff to digest...

OK I have tried all of the above and yet I still get the lack of memory error. I looked at the partition namger and there is lots of free memory about 60Gb but I don't really understand how that disc partitions work. Please bear in mind I'm a newbie and not all that knowledgable!!

oops! had a few drinks...I think I had to repartition my hard drive when I did all that...