Depends on what you are upgrading from.
I have read an article that says one can upgrade to Win 8.1 from Win 7.
I don't know if there is different procedure or not as I have not done that.
One thing I do know is upgrading from Win 7 to Win 8.1 will wipe out all 3rd party programs.
However, I did upgrade my Win 8 Pro to Win 8.1 Pro.
When the upgrading started I was asked to choose one of the options.....
1. keep personal files and settings
2. keep nothing.
I chose option #1
Results : all my files, settings as well as 3rd party programs are retained intact, except those that are not supported by 8.1, such as Avast.