Again, please use the text area to ask your question, also which version of
PowerPoint your using.

Hi,

If you are using 2003 - select a slide you want in the new design style and
choose View, Taskpane if necessary.

In the task pane open the drop down arrow at the top right of the pane and
choose Slice Design.  Find the slide design you want to apply and click it
once, then open the drop down arrow on the right and choose Apply to
Selected Sides.

Of course this question is not quit clear - this may not be what you want
since you choose the word theme, but you didn't include the version of
powerpoint you are running so...

cheers,
Shane Devenshire