1. Open the template and save current theme to a location you manage to find it later.
2. Open a ppt that need to change theme ,right click and select format background
3. Tick hide background graphics and clcik reset background
4. Click ''Apply to all" ...Now you can see all the template become blank
5. Go to tab "Design" and click "Browse for Themes" . Select the theme u save at step 1.
6. Right click "format background" ,un-tick "hide background" and Apply to all
7. Now u can change your layout .Use ctrl key or shift key to apply the template that using same layout for your work easily.Thanks.