Every Keynote theme includes different master slide layouts. To quickly change the look of a slide, you can apply a different master to it. You can also turn body text and title placeholders off to hide them on a slide.
You can also choose a different theme for the presentation.
Select one or more slides in the slide navigator.
Click the Change Master button near the top of the sidebar on the right.
If you don’t see a sidebar, or the sidebar doesn’t have a Change Master button, click 
in the toolbar.
Select a different slide layout.
Tip: You can add a Masters button to the toolbar, which gives you quick access to all slide layouts. To learn more, see Customize the toolbar.
Select one or more slides in the slide navigator.
In the sidebar on the right, select or deselect the checkboxes next to Title or Body.
If you don’t see a sidebar, or the sidebar doesn’t have Title and Body checkboxes, click in the toolbar.
You can change the theme of a presentation at any time. Your existing slides inherit the attributes of the new theme, including object styles, title styles, and more. If you customized anything on your slides—for example, if you changed slide backgrounds or the color of text—you can choose to retain those changes.
Note: You can’t change the theme of a presentation you’re sharing with others.
Choose File > Change Theme (from the File menu at the top of your screen), then select a new theme.
Deselect the “Keep your style changes” checkbox if you want the new theme styles to override your style changes.
Click Choose.