PowerPoint 2011 for Mac provides users with the option to replace font based on the font name. If you want to change font for couple of words then you can select those occurrences and change the font using the option available as part of Home menu.
And if you want to replace lots of occurrences of words of specific type of font then manually replacing the fonts will be a tedious job.
Find and replace font based on font type.
Click Format menu and select Replace Fonts option.
In the Replace Font screen, select the Font that needs to be replaced in the first drop down then the font with in the second drop down.