How do I add new templates to an existing PowerPoint presentation??

I am trying to add new templates that I just DL'd from the Internet to an existing PowerPoint presentation my boss has asked me to spruce up tonight for a meeting tomorrow. How do I add them in???

Whenever I try, the new slide that gets "created" matches the ones already existing in the presentation and does not look like the new one I am trying to Insert.

Can anyone help??

I am on a serious deadline here and do not know what to do. Have used the Help button. Have trolled all over the Internet, including the Microsoft sites. SOS!!!! Thank you!!

How do I add new templates to an existing PowerPoint presentation??ie tab

1. Click on the menu item called, "Format" then

2. select "Apply Design Template."

3. Select one of the new templates.