How would you replace Ubuntu?

[FJGamer]

If I wanted to reinstall the OS over its current installation without losing the files (no partitioning), how would I do so?

This is hypothetical. I'm not wanting to do such a thing. I was just thinking about it, because I do the same thing sometimes when I have to recover Windows.

[lswest]

You can choose to install Ubuntu, and at the partition screen choose manual, set up all your old partitions with mountpoints, don't format. It should re-write system files (it may also thoroughly mess up your system). I would suggest just using a seperate /home partition and backing up tweaked system files.

[Bakon Jarser]

Without partitioning I think your options are to use something like remastersys to make a complete copy of your install.