If you choose to "Keep nothing" when you upgrade to Windows 8.1, your personal files will be temporarily saved to the Windows.old folder (unless you formatted your hard drive before installing). If you decide that you want some or all of these files back, you can usually retrieve them from this folder.
You can run a troubleshooter that will automatically retrieve your personal files from the Windows.old folder and copy them back to their original location. The troubleshooter will work on all languages, but the text in the troubleshooter is only in English.
Run the recover personal files troubleshooter.
Swipe in from the right edge of the screen, then tap Search.(If you're using a mouse, point to the top-right corner of the screen, move the mouse pointer down, then click Search.)
Enter Computer in the search box, then tap or click Computer in the search results.
Double-tap or double-click the drive that Windows is installed on (typically, the C: drive).
Double-tap or double-click the Windows.old folder.
Double-tap or double-click the Users folder.
Double-tap or double-click your username.
Open the folders that contain the files you want to retrieve.
Copy and paste the files that you want from each folder to a folder in Windows 8.1.
Repeat steps 5-7 for each user account on your PC.