To add new images to a photo gallery or slideshow:

1. Click the photo set on your page.
2. Click Manage Photoset from the pop-up menu.
3. Drag and drop images from your computer or click the Add Images in the top-right corner.
4. The images will be added to your photoset.

To remove images from a photo gallery or slideshow:

1. Click the photo set on your page.
2. Click Manage Photoset from the pop-up menu.
3. Hover your mouse over the image you want to delete.
   
4. Click the three dots at the top right corner of the image. Click Delete.
   
5. A warning message will pop up. Click Delete.