It used to be in Personalization under themes. It permitted you to open the current theme and edit (add or remove pictures) from the theme. The function seems to have been left out in Windows 10, and was available in previous Windows versions.
Maybe the Gods at MS will here our cries and return this functionality
You mean the desktop background? Right click on the desktop, and select Personalize. You should get the screen below where you can add/change the picture.
Workaround: Once the theme is created, the pictures are stored in subfolders under the (hidden) <USER>\AppData\Local\Microsoft\Windows\Themes folder. You can add or remove pictures from these subfolders and get functionality similar to what was available in the Theme settings in the good old days.
Is it possible to edit the .theme files (from windows 7) to change the path of the pictures?
At first glance it seems easy:
[Control Panel\Desktop]
Wallpaper=E:\
but even with the new path added while the files are still in the old location; it is must be using the old location. I just temporarily renamed the folder for the current theme and as expected the slideshow halts as it can't update the file in:
C:\Users\SgtSixpack\AppData\Roaming\Microsoft\Windows\Themes
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I found how to make themes editable (works according to this user):
Problem in theme editing with notepad Solved - Windows 7 Help Forums
Although this is for windows 7, maybe with the classic personalisation hack it can be used in windows 10.
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