What if you want upgrade to Ubuntu 12.04 (Precise Pangolin) from 11.10 (Oneiric Ocelot) but can’t do over the Internet? Maybe your connection is not fast enough or just not reliable to perform the upgrade. Well, you can always upgrade using a CD/DVD ISO image.
If you have access to faster more reliable connections like from a library or school, download the image from Ubuntu site and burn it onto a CD/DVD. Then when you get home use it to upgrade your system. This brief tutorial is going to show you how to do it.