Do you have any removable media to save the settings on?
Do you lose/re-create your home directory when upgrading?
Is /home a seperate filesystem (mount point) or a part of the root filesystem (/)?
If /home gets overwritten, then you will probably need to back up a fair bit before the upgrade.
Most files that you might need to re-create / restore (if not in /home) are likely to be in /etc
Therefore you may want to start by:
tar cf /media/usb_disk/my_backup.tar /etc /home
(assumes you have a USB disk mounted on /media/usb_disk and that there is enough storage to complete the tar)
*** This is the minimum I would do before upgrading! ***
Depending on what you have installed and what settings you normally need to change you may need to backup different areas!
to list the contents of a tar file:
tar tf /media/usb_disk/my_backup.tar
(note that the lead / has been removed from the file.
restore a single file from a tar file (to a different place):
tar xf /media/usb_disk/my_backup.tar -l etc/passwd etc/shaddow
This will create two files /media/usb_disk/etc/passwd and /media/usb_disk/etc/shaddow
These can be compared to the existing files or can replace the existing files (be very careful when replacing system files!)