Open the PicFindr app.
Click on any image.
Click on the “Set Desktop Picture” button on the Sidebar (the Sidebar for the image will be opened on the right side of the app interface after you click on the image).
Wallpapers would be changed automatically.
Or:
In the Sidebar hover your mouse over the image >>> the "Preview" button will appear.
Click on the “Preview” button.
In the image window, click on the "Set Desktop Picture" button.