Mobile & Desktop Wallpapers
Instructions - iPhone/iPad
Save the image to your device's photo gallery, then go to Settings and Wallpapers. Browse to the image, and set it as either your Home or Lock screen wallpaper (or both). You can move or zoom in on the image, but if you select the right one for your device it should line up perfectly with your screen.
Instructions - Android phones
Save the image to your device. From the Settings menu, choose Personalize or Display (varies depending on device) and Wallpaper. Choose the image from your gallery. If your screen resolution matches the image size it should centre on your phone, but otherwise you may need to scale or adjust.
Instructions - Nexus 7
Save the image to your device. Touch and hold an area of your home screen without an icon or widget on, and tap Gallery to select the image from there. The cropping box will display over the image - you may wish to adjust this but if you leave it as the default, it should give the best results (ideally the "reddwarf.co.uk" logo will appear just above the dock on your centre-most home screen).