Delete for the plist files for Slingplayer. I think that's where the Mac's keeps their preferences.
If you're feeling really techie and want to remove all supporting files such as your Slingbox directory settings and favorites, you can find these files within the Preferences folder of your Home Directory (HD>Users>your User folder>Library>Preferences):
Now that you have removed all files, reinstalling your SlingPlayer will result in a totally clean installation of the application and new settings will be created again.
We hope you don't leave SlingPlayer off your Mac for too long!