Keep old GUI on rel. 13

[taxidimu]

I am ready to upgrade my Ubuntu Server 12 and LUbuntu desktop 12 to release 13.
But I want to keep the present GUI, not to migrate to the new one.
How can I?
Thank you.

[grahammechanical]

What new GUI? Ubuntu server does not have a GUI and Lubuntu will still have the same user interface, I am sure of it. I am not sure if a Ubuntu server upgrade will upgrade that Lubuntu desktop.

[taxidimu]

I mean UNITY.
On my server I have installed GNOME (because I use it as a desktop, sometimes). On the clients I have GNOME too.