On Your iPhone and iPad
Go to alphagammadelta.org/wallpapers on your iPhone or iPad. Select the iPhone or iPad link for whichever background you would like. Once the image opens, hold your finger down on the image until the "Save Image" option appears. Click on "Save Image" and exit Safari. Open your Photos app and open the image of the background you just saved. At the bottom, click on the arrow button in the left hand corner, then choose "Use as Wallpaper."