Changing dots per inch (DPI) in Powerpoint Office 2011 for Mac

I want to increase the resolution of my images in PowerPoint for (2011 for Mac). In other forums it says to go to Preferences -> Save and from there you can change the dpi...here's a fuzzy screen shot of what it should look like:

Here's what I have:

Please let me know if there is another way to increase the resolution/dpi of an image.

thanks!