Why Upgrade Linux?
The first type of distribution upgrade we will look at is an actual upgrade. Any distribution upgrade takes the currently running version of your operating system and upgrades all applications (from the kernel to the user space applications) and upgrades each and every piece of the puzzle. On top of upgrading all of the applications, a distribution upgrade will get and install (or upgrade) all necessary dependencies.
One of the best reasons to upgrade is the retention of all user data and files. In theory an upgrade will not effect any user data; which means, upon completion, the user will be able to log on as usual and all of their files and configurations will have been retained. This becomes the obvious choice (over a fresh installation) when the user has a lot of important data and/or configurations on the machine.
Of course a distribution upgrade is only possible when you are upgrading from one release of a distribution to another. For instance: You are running Ubuntu 8.04 and want to upgrade to Ubuntu 8.10.
Why Choose a Fresh Linux Installation?
The primary reason you would want to do a fresh installation over an upgrade is if you are undertaking a major upgrade. There are two types of upgrade: Major and Minor. A Major upgrade is moving from Ubuntu 7.10 to 8.04. The "Major" factor is dictated by the major version number which is the number prior to the decimal point. A minor upgrade would be moving from 8.04 to 8.10.
The primary reason one would not want to do a major upgrade is that often the upgrade deals with serious changes to the operating system. A minor upgrade generally only offers smaller improvements over already existing technologies. Many times doing a major upgrade can result in a number of broken packages and can render the system unusable. These cases are not 100%, but better safe than sorry.
How to Upgrade Linux
Doing an update is generally quite simple. We'll use Ubuntu as an example. Go to the System menu and select Software Sources. You will have to enter your password to continue. A new window will appear that will have four tabs along the top. One of those tabs is labeled Update. Click on the Update tab and select Normal Releases from the Show New Distribution Releases drop-down. Now close this window by clicking the Close button.
Open the Update Manager (from the System menu go to the Administration sub-menu and select Update Manager) to reveal an Upgrade button indicating a new release is available. Click the Upgrade button and then click the Upgrade button on the Release Notes window. All you have to do now is sit back and wait for the upgrade to complete.
If you're new to Linux, the following articles might be of help in your quest to upgrade:
Desktop Linux: GNOME