One of the benefits of using Apple's Keynote slideshow software is that it has built-in themes that you can use to customise your presentation and give it a more distinct look and feel. When you create a presentation on a Mac, you can cycle through themes quite easily. However, on an iPad, all theme decisions are final, which means the only way to change the theme on an iPad version of Keynote is to copy all of the slide information into a new presentation which features the theme you want to use.
Open a new presentation in Keynote. Tap the theme you would like to use from the list that automatically pops up when you open Keynote.
Tap "File," "Open," and then tap the old presentation of which you want to change the theme. Tap on the first slide you wish to copy. Hold your finger there until the slide begins to vibrate. While holding your finger on the vibrating slide, use your other hand to tap on all of the other slides you wish to copy. Remove your hands from the screen.
Tap one of the slides, and then tap "Copy" from the context menu.
Tap a slide in your new presentation and tap "Paste" from the menu that appears to paste the copied slides into the new presentation.
Adjust various aspects of your new presentation to match your new theme. These adjustments can include changing the font type and colour, as well as moving various aspects of the slide around into their proper location.