Must I uninstall an older version of Ubuntu before installing a new one

What version do you have now and what version do you desire?

My apologies for not replying to you sooner. The version which I have installed and cannot update is Ubuntu Linux 10.10 and the one I have downloaded and would like to install is Uuntu 12.04 Do I have to uninstall the 10.10 first and if so how do I do it.
Regards. Antony Bristow

I suggest you remove Maverick first, then install Precise. You will get to Precise quicker and have a cleaner OS than all the upgrading you would have to do. You can retore user data from backup

Thank you for your answer. By 'Maverick' I assume that you mean Ubuntu 10.10 and you suggest that I remove that first. But that was part of my original question. HOW DO I UNINSTALL OR REMOVE IT ?

Yes Maverick is Ubuntu 10.10

If you have Only Maverick installed then I suggest you simply boot to the Precise liveCD and tell the installer to use the whole disk space. It will wipe out ALL data and install the OS, you can then restore your user data from backup.

If you dual boot, the easiest way is to run gparted in the liveCD and delete the Linux partitions then run the installer. You can then install to the free space and the dual boot should be resetup again.

Thank you very much indeed for your e-mail and I do much appreciate your help. I'm very sorry to be such a nuisance but I'm still having difficulties. You say 'run gparted in the live CD' but what do you mean exactly. I put the CD in the machine and then start it up. I'm offered one of three choices:- Ubuntu withg Linux Generic, Memory Test or Windows XP. If I leave it the screen goes to Ubuntu and what looks like a blank Desktop with @Application,Places, System and the date at the top. What then - I'm stuck. Regards. Antony Bristow.

Do you dual boot the system or is Ubuntu the ONLY OS in the system?

Dual boot. In my last message to you I explained that when I open up I am offered three choices : 1/ Ubuntu with Linux Generic 2/ Memory Test and 3/ Windows XP

ok then in XP disk manager you can delete the Linux partitions to leave free space, you can then install to the free space.

I very much appreciate your efforts to assist me but we seem to be going round in circles. You keep saying 'delete the Linux Partition' but HOW. Thats what I want to know - HOW DO I DELETE THAT PARTITION.

Windows disk manager

Still problems I'm afraid. I've managed to uninstall the old Ubuntu via the disk manager but when I insert the disc and switch on again all I get is a screen saying 'grub rescue'
What does that mnean and what do I do.

Well yes, you deleted Grub's config. You need to boot to your Precise install CD now.