Make sure to backup your saves or better yet, the entire game directory before updating.
- You can update from an older UPU version.
- You can install UPU on top of UP 1.02.31 to make use of the fixes.
In both cases, you won't see some of the fixes on already visited maps. Other than that, savegames should be compatible, but no guarantees.
If you made any changes to ddraw.ini, these changes will be lost when you overwrite that file. If you want to preserve them, make a backup copy and then transfer the settings manually to the new ddraw.ini.
The same goes for mods\mods_orders.txt. If you altered that file, you'll have to transfer the changes manually. You can find the old file in backup/mods_order.txt inside game directory.