Add or replace masters using existing design templates

Switch to the slide master view.
- Choose View → Slide ? Master.
Open the Slide Design task pane.
- Choose Format ? Design.
To replace masters, select the master(s) you want to replace in the thumbnails on the left.
In the Slide Design task pane, point at the design template you want.
Click the design template's drop-down arrow and choose one of the following:
- Replace Selected Designs: replace all selected masters with the selected design template.
- Replace All Designs: replace all masters in the presentation with the selected design template.
- Add Design: add the selected design template as a master.