The next Ubuntu version 11.04 Natty Narwhal is coming soon, if you intend to upgrade to 11.04 from current Ubuntu version there are 4 ways you can choose including online and offline upgrading.
Note: Make a backup of the sources, softwares, and important data, upgrade may cause something incompatible.
1.) GUI upgrading with update-manager
This is the most normal way to upgrade Ubuntu to next version, just run this command to launch update-manager:
sudo update-manager -d
You can see this window with available Ubuntu release, click Upgrade to start.
2)upgrading in command line interface(CLI)
Edit /etc/update-manager/release-upgrades by
gksudo gedit /etc/update-manager/release-upgrades
save the file and then execute:
sudo do-release-upgrade -d
it asks to change sources in source.list while upgrading, just enter y and it upgrades automatically.
3.) Since Ubuntu 11.04 Natty, Ubuntu Live-CD supports upgrading from the previous Ubuntu installation. Download the Ubuntu 11.04 iso and create a Live-CD or Live-USB, then boot from the device, if you have a Ubuntu installed on machine there’s an upgrade option in the installation guide
4.) offline upgrading using alternative iso
Download the alternative iso image(not normal iso image) from: http://cdimage.ubuntu.com/daily/current/
Then mount the image(change PATH/TO/ISO):
sudo mount -t iso9660 -o loop PATH/TO/ISO /cdrom
Finally, start upgrading with: