General Upgrade Information
An upgrade is the process of going from an earlier version of Ubuntu to a newer version of Ubuntu. An example of this would be going from Ubuntu 6.06 (Dapper Drake) to Ubuntu 6.10 (Edgy Eft). Skipping versions is not advised and can cause a lot of damage to your installation. If you are using an earlier version, and want to 'skip' a version, the only safe way is to backup your data and do a fresh install, or to progressively upgrade to each successive version. An example of this would be if your are running 5.10(Breezy) and want to upgrade to 7.04(Feisty) you would have to first upgrade to 6.06(Dapper) and then upgrade to 6.10(Edgy), and then again to 7.04(Feisty) or simply do a clean/fresh install of 7.04(Feisty). An easy way to test a newer version of Ubuntu on your machine for compatibility is trying the Live CD (Desktop CD) before upgrading.
It is generally recommended that you run the latest version of Ubuntu as there is always added support for new hardware, and is usually more optimized/faster. The LTS version is recommended for people in an environment(generally commercial/industrial) that want to keep the same version for a longer amount of time and do not require newer/faster/updated versions, but instead do not want things to change.
Using packages from repositories not controlled by Ubuntu is not recommended as it can be a security risk and may break or complicate your upgrade. If you have used EasyUbuntu or Automatix which are both not recommended nor are they supported, you may have problems upgrading to a newer version and require a fresh install.
Supported (Current) Versions
Supported versions of Ubuntu have finished their testing and are reliable and recommended for every day normal use. This is what you would usually have installed on your machine.
From 6.06 to 6.10
Version: 6.10 (Edgy Eft)
See the EdgyUpgrades page for upgrading information.
From 5.10 to 6.06
Version: 6.06 LTS (Dapper Drake)
See the DapperUpgrades page for upgrading information.
LTS stands for 'Long Term Support', it is supported for three years as a desktop and five years on a server. By supported it means that Ubuntu will continue to provide security updates etc for the entire term of 'support'
From 5.04 to 5.10
Version: 5.10 (Breezy Badger)
See the BreezyUpgradeNotes page for upgrading information.
Unsupported (Obsolete) Versions
End-of-life releases have been supported previously but have reached the end of their support cycle. It would be best for users of these versions to upgrade as they are obsolete and you will not be receiving support for these versions, for example no more security updates will be provided.
From 4.10 to 5.04
Version: 5.04 (Hoary Hedgehog)
EOL: October 31, 2006
See the HoaryUpgradeNotes page for upgrading information.
Version: 4.10 (Warty Warthog)
EOL: April 30, 2006
Current Development Version
Development versions are still in a testing phase, and only developers and testers should install these releases as they are NOT stable enough for production(everyday) use.
6.10 to 7.04
Version: 7.04 (Feisty Fawn)
Projected Release Date: April 19, 2007
See the FeistyUpgrades page for upgrading information.