Sstrhsrtj

I use Ubuntu 10.04 for more than a year and I often feel that I need to reinstall it to newest version.

I'd like to take most of my configurations and important settings to the new system. I already have some files and directories in mind that I certainly want to backup, but I'm afraid I will forget something.

Is there some checklist, guideline or even software I can use to help me with backing up the important data? I don't want to backup the whole partition. (it's not so critical)

How can I cleanly update to a newer version?

As psusi correctly points out, you shouldn't need to reinstall a Debian derivative. Just upgrade.

Regardless, the obvious answer to the backup question is to use version control to back up your home directory and config settings. For the config files in /etc on a Unix-like system, Joey Hess's etckeeper is popular. I'd recommend using a distributed version control system like Mercurial or Git, which can be used to periodically push the repository contents off your hard drive, and thus acts as an automatic backup. With Mercurial you can set up a
post-commit hook which will push after you commit, so your backups always stay completely up to date.

Note that this is not a general backup solution in this case, but works well for important config files and so forth, since they are general small text files, and therefore ideal for source control. And in this situation distributed version control is super-efficient, comparable in performance to rsync but better because of the atomicity of version control. Mercurial, at least, will roll back rather than push a partial changeset, and I imagine Git does the same. Also, version controlling your config files has obvious additional benefits.

You don't need to backup anything. Just install the new version and choose the option to upgrade the existing install. All of your files and settings will be preserved.

I'd recommend apt full-upgrade or - if you like the more "back in those days" way - apt-get dist-upgrade.
You can look at man apt and man apt-get for deeper information and more options.

For me, this totally works every time. You don't need to backup anything while it's way faster than backing up anything and re-setting up a whole system - even without all the costumization made over time. You also don't need to manually install afterwards all your packages your added over time to your system.

In my opinion, this is the most elegant way among the few and also the most efficient way indeed to "cleanly update to newer version" of a Distro with fixed releases (not rolling).