Upgrading to Ubuntu Lucid Lynx is quick and easy. There are two methods available for the upgrade. You can either do it online or, you can use the Alternate Install CD from Ubuntu.
If you prefer to do it online, follow this step by step guide here. Though, if you do not have a reliable internet connection, a better option is to do it offline. To start with, get hold of the Alternate Install CD.
First download the ISO from this location. Now you have three options. Burn the Alternate CD ISO to a disk, transfer it to a thumb drive or mount the ISO locally.
If you choose the last option, mount the ISO with this command:
sudo mount -o loop /dir/ubuntu-10.04-alternate-i386.iso /media/cdrom0
Here “dir” is the path to which you have copied your Alternate Install CD ISO.
As soon as the mount is complete, a dialog will pop up asking you to upgrade. Complete the steps and let it install. This will upgrade your system to Ubuntu 10.04 Lucid Lynx LTS. Enjoy.