How can I resume an upgrade after denying it the first time?

Last evening i started the procedure to upgrade ubuntu 11.10 to 12.04 while not being at home and with a slow connection. During the upgrade procedure ubuntu told me that the required time with my connection was very long. Because of lack of time i decided to deny the upgrade and start it today, but today i can't find how to start it again because the upgrade button is not anymore visible !

What can i do to upgrade ubuntu without downloading the iso? Is there any terminal command that allow me to start the upgrade ?

Start update manager and there you will find a button so you can upgrade.

If not you need to enable update manager to look for dist upgrades see: Update manager doesn't offer an upgrade to the new release

Type this in Terminal

 update-manager -d