Here's how you can choose the default application to open a file in OS X Mountain Lion. 1. Select the file. 2. Press Command + I on your keyboard (or select File then Get info from the file's menu in the menubar). 3. Go to the "Open with:" tab. 4. Select the application you want to use to open the file. 5. If you want your change to apply to all files of that type, click the Change All button.
Use the Get Info window in Mac OS X | Daily Mac Tips