Make no mistake about it, Windows 8.1 is a complete upgrade and not just an update, it completely wipes your Windows 8 install and gives you a new windows operating system. Do some research in case things have changed since February when I did this. With that said it is a necessary upgrade, without it you will eventually experience lots of crashes and failed updates as the Windows Update in ver.8 is really, really buggy.
From my experience with upgrading to 8.1 you will want to backup all your content, especially the Public/Documents/Reallusion folder. In fact I'm guessing you also have DAZ installed so if you just backup the Public/Documents folder you will save all that content as well. I also had content in my personal user documents folder and that should be backed up as well.
I failed to do that and lost all my custom files, both DAZ and Reallusion files, months of work all gone in a matter of seconds! Reinstalling the programs wasn't a big deal but not finding any of my custom files was a sad, sad thing.
Sine that happened I now use the Windows 'File History' feature found in the 'Control Panel' and back up to an external drive. This is a pretty good program but not fool proof, it is Microsoft after all. As a second option I spent a couple days playing with other backup programs to find one that was free, user friendly, reliable, and accurate.
The one I found that met all the above is AOMEI Backupper Standard 2.0.2 found here:
http://www.backup-utility.com/free-backup-software.htmlIt's a silly name but it works! I tested it as I did all the others and it repeatedly reinstalled my content intact exactly where it should be. This was also to an external drive by the way.
For the best advice I could find on Windows 8 to 8.1 I found here:
http://pcsupport.about.com/od/windows-8/fl/windows-8-1-update-1.htmTons of info and step by step tutorials on how to update correctly, only wish I had looked there first.
I hope this helps you, I don't want anyone else to lose months of custom files like I did!
Dell XPS 8900, Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz, 3408 Mhz, 4 Core(s), 8 Logical Processor(s), 16 GB RAM, - 4 GB GeForce GTX 745, NVIDIA compatible.
Acer Aspire V Nitro Laptop, 2.5GHz Intel Core i5-7300HQ processor with 6MB cache, 256GB solid state drive, 16GB Ram, 4 GB NVIDIA GeForce GTX 1050 Ti graphics.