I was terrified that I would lose all the programs that I had installed over the last few weeks. Ran a Belarc Advisor to get a list of my laptop’s specs and all the software I had installed.
If your laptop came with Windows 8, and you got the Windows 8.1 upgrade from the Windows App Store, you should be okay. (But I went ahead and copied all the .exe files that I used to add programs to my laptop. Always good to backup your junk.)
Took about an hour to download the upgrade, and another hour to wait for this thing to upgrade.