On your iOS device, do the following to install a theme from these sources:
iCloud: If Keynote is set up to use iCloud on your device, your theme appears in the presentation manager and is identified by a theme badge. Tap the template thumbnail, then tap Install.
Note: If you upgrade your account to iCloud Drive, syncing may not work in all cases, depending on which versions of OS X and iOS you have installed. See this Apple Support article for more information.
AirDrop: Swipe up from the bottom of the screen to open Control Center, then tap AirDrop. Tap a discovery option, and when the AirDrop message appears, tap Add.
An email: In Mail, tap the attachment, then tap the screen. Tap
at the top of the screen, tap Open in Keynote, then tap Add.
A WebDAV server: Download the theme from the server, then tap the screen. Tap
at the top of the screen, tap Open in Keynote, then tap Add.
The theme appears in the My Themes category in the theme chooser.
To learn how to use a WebDAV server with your iOS device, see Use a WebDAV server to store presentations. To learn how to transfer files using iTunes, see Use iTunes to transfer files.
In the presentation manager, tap Create Presentation, tap the custom theme name, type a new name, then tap Done.
In the presentation manager, tap Create Presentation, touch and hold the custom theme thumbnail, then tap Delete.