Although there were no problems when I upgraded my machine to Windows 10 (
other than a few brightness and driver issues[
^]). All of my documents, photos and user settings were still present and the license key was automatically applied.
I would still recommend, (because I was using Windows 8.1 and a
pre-licensed machine[
^]) so there were no problems, although it took at least 2 hours to download and install the upgrade. I would recommend, that you create a backup of your data. Remember to back up the projects and other few things. Hopefully, Windows won't mess up with the folders and files. But still, there are enormous cases in which Windows show up, "
Something Happened" which is a reason to always take precaution and save your data.
Other than that, you will also get a few problems with your device drivers. Try looking for a few drivers in the Windows Update.
Good luck with your upgrade. Before that, please take some time to read this answers thread.
http://answers.microsoft.com/en-us/insider/wiki/insider_wintp-insider_install/frequently-asked-questions-windows-10/5c0b9368-a9e8-4238-b1e4-45f4b7ed2fb9[
^]