Summarize:

This is done using steps 1 - 4 in Method 1 (Changing the Screensaver).    It’s located towards the top-right of the Photos Screensaver Settings menu. This is done by clicking on the folder that contains photos you want to update your screensaver with.  This is done by clicking on the dropdown menu to the right of “Select a slideshow speed”.  This makes the photos appear in a random order. Your photos’ settings will be updated. The changes will be applied and your screen saver will be updated as a slideshow of personal photos.
Open the Screensaver Settings menu. Click the dropdown menu under “Screensaver”. Click on Photos. Click Settings. Click on Browse. Add a folder to the Screensaver dropdown menu. Click OK. Set the speed at which photos appear. Click on your preferable speed. Check the “Shuffle pictures” box (Optional). Click Save. Click OK at the bottom of the settings menu.