You can't. The Ubuntu update manager does not offer the option to upgrade from Ubuntu 11.4 to 12.4. You have to waste 750 megabytes of download upgrading from 11.4 to 11.10 then duplicate the effort with an upgrade form 11.10 to 12.04.
I tried to update my netbook direct and I had to go through the slow crunch, crunch, crunch of the 11.10 upgrade first, complete with broken support for the touchpad. Luckily the keyboard worked.
My suggestion is simple, skip the Ubuntu Update Manager. Download 12.4 to CD, or USB stick, then install from CD. You save nearly a gigabyte in duplicate downloads and you have a CD backup to slip in your file for your computer. you can then use the CD for your other computers.
The upgrade from 11.10 to 11.4, 2 hours on broadband, was very slow compared to the upgrade from 11.4 to 11.20, at under an hour. I think the 11.10 servers have far less use than the 12.4 servers. When you are upgrading several machines to the latest version of Ubuntu, the download to CD will save you repeatedly waiting for the upgrade download.
Another hint. I used a wireless connection using a super high speed trick wireless hub device with the netbook near the hub so it gets 100% of the bandwidth. It does not. Wireless bandwidth is always limited and always shared and always inefficient. A wired connection would have been the minimum of five times faster. When you use a good brand of wired switch, the switch does not share, everything has a separate path and runs at maximum speed. On a wired connection, everything is faster and consistently fast.
If you install from a USB stick, buy a good fast one. The fastest small sticks cost only a few dollars more and they are 20 times faster, saving you many dollars of time of time every time you use them.