Ubuntu (Jaunty) or 9.04 ubuntu ubuntu is the latest version of ubuntu 8.10 (Hardy). Before you begin upgrading ubuntu ubuntu 8.10 to 9.04

You can only directly upgrade to Ubuntu 9.04 Beta from Ubuntu 8.10

Before You Start

You can only directly upgrade to Ubuntu 9.04 Beta from Ubuntu 8.10 (see UpgradeNotes).
Be sure that you have all updates applied to Ubuntu 8.10 before you upgrade.
Before upgrading it is recommended that you read the release notes for Ubuntu 9.04, which document caveats and workarounds for kn
own issues in this version.

If you have a version of Ubuntu which was released before Ubuntu 8.10, please see UpgradeNotes for information on how to upgrade.

Network Upgrade for Ubuntu Desktops (Recommended)

You can easily upgrade over the network with the following procedure.

1. Press Alt-F2 and type update-manager --devel-release

2. Click the Check button to check for new updates.

3. If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete.

4. A message will appear informing you of the availability of the new release.

5. Click Upgrade.

6. Follow the on-screen instructions.

Network Upgrade for Ubuntu Servers (Recommended)

Install update-manager-core if it is not already installed:
```
sudo apt-get install update-manager-core
```
Launch the upgrade tool:
```
sudo do-release-upgrade --devel-release
```
Follow the on-screen instructions.

Upgrading Using the Alternate CD/DVD

Use this method if the system being upgraded is not connected to the Internet.

Download the alternate installation CD
Burn the ISO to a CD and insert it into the CD-ROM drive of the computer to be upgraded.
- If the ISO file is on the computer to be upgraded, you could avoid wasting a CD by mounting the ISO as a drive with a command like:
- mount -o loop ~/Desktop/ubuntu-9.04-beta-alternate-i386.iso /media/cdrom0
A dialog will be displayed offering you the opportunity to upgrade using that CD.
Follow the on-screen instructions.

If the upgrade dialog is not displayed for any reason, you may also run the following command using Alt+F2:

gksu "sh /cdrom/cdromupgrade"

Or in Kubuntu run the following command using Alt+F2:

kdesudo "sh /cdrom/cdromupgrade"

Upgrading from a Torrent

If you're familiar with torrents and have an ISP that doesn't limit them, you can download the upgrade much more quickly. You'll also be sharing your bandwidth with other Ubuntu users and helping to reduce the load on the servers, which is especially beneficial on release days when the server overload causes problems.

Just visit http://releases.ubuntu.com/jaunty/, and download the appropriate torrent file for the alternate installation CD, found in the list towards the bottom of the page. (It will have a filename like ubuntu-9.04-beta-alternate-i386.iso.torrent.) Load it into your BitTorrent client, and after it is done downloading the ISO, follow the alternate CD upgrade instructions.

Detailed instructions here and here.

Sources : https://help.ubuntu.com/community/JauntyUpgrades