There are two methods to change the wallpaper: from a photo viewing application (Gallery, Picasa, etc...) or from the home page.

Via an application, you will usually need to select a photo, open the settings menu and choose the option that will let you set it as your wallpaper.  

The best way is to set your wallpaper direclty from the home page. Long press on the screen in an empty zone of your home page. A new menu will open, displaying different options:  

1. Select your wallpaper in the application Gallery (preinstalled Google™app) 

2. Select an animated wallpaper (see below) 

3. Select your wallpaper via a third-party application. You will have several icons depending on the preinstalled apps on your device. 

4. Select your wallpaper among the ones preinstalled by default in your device. 

Whether you use the Gallery app or another third-party application, you will need to resize your wallpaper so that it matches Android ™ standards.

The lighted part in the frame represents the main page of the home screen in portrait and landscape orientations, while darkened parts represent the extension of your home screen when you scroll left or right.
To increase/decrease the frame size, hold one of the blue dots and drag in the desired direction. You can also move the frame to target a specific area by pressing anywhere in the frame and dragging.

The preinstalled wallpapers are already well sized to match your display, no additional operation is required. 

The animated wallpapers are preinstalled applications as any others preinstalled apps such as Settings and Gallery. You will be able to set different options such as frame rate, the number of displayed items, etc....

You have access to other animated wallpapers via Google Play ™. They will be listed in the same place as those provided by default with your device.

 Please note that the use of an animated wallpaper can increase battery consumption and slowdown your system.