Source:
http://www.ubuntu.com/testing/dapperbeta?highlight=%28dapper%29
Upgrading from Ubuntu 5.10
A new version of the Update Manager application has entered breezy-updates which can upgrade your entire system in a few simple steps.
To perform the upgrade:
1.
Update your system to ensure that you have the latest version of Update Manager and associated packages. The necessary versions are available from the breezy-updates repository, which is enabled by default.
2.
Run the following command (either via ALT-F2 or a terminal):
gksudo “update-manager -d”
*
The “-d” switch instructs Update Manager to consider pre-release versions, including this Beta release. Without this switch, only official, final releases will be considered.
If you have a working network connection, it should then inform you about a new release and offer to upgrade your system.