I click on "install updates" and get a window;-
Another application seems to be using the package system at this time. You must close all other package managers before you will be able to install or remove any packages.
As far as I can see no other applications are running (I've just booted)
I've tried "sudo apt-get dist-upgrade" suggested by JoKeR. This appears to work, but I get left with a EULA window which I can't get rid of except by closing the console window. This doesn't seem right to me.