[pessimizer]

> And can I convert an Ubuntu into a Debian by reinstalling it while keeping my home directory?

You can do that with any distribution, unless you expect your configs to line up exactly.

If you don't keep your /home on a separate partition, back it up. Install Debian, making sure to separate /home and root into different partitions this time. Go through your ~/.configs, find the ones you've changed (most of this will probably be browser shit) and put copies aside. Then take all of the configs out of your home directory backup (including the originals of your changed configs) and put those aside in a different place, deleting them from the backup of your home directory. Backup the virgin ~/.configs from your new install (do not delete them from the new home directory.) Then copy your old home directory files (sans configs) over your new ones using rsync. Compare your manually changed files to the virgin files from the install - has the format changed, will they still work? Are they located in the same directory in Debian as in your previous distro? If it looks fine, copy them in. See if they work. If they don't, look up why not. They probably will.

If you keep your home on a different partition, then install as if you don't, and let Debian create a home in the same partition as the new OS. Do the same config dance as above (annihilating your old configs other than the customized ones), and switch your /home to be mounted from your old home partition.

Or at least this is what I do. On your desktop, you probably want to install testing, on your servers stable.