When working in the Filter Gallery, you can hold the Ctrl Key (Mac: Command) to turn the “Cancel” button into a “Default” button. Click the default button and the factory-set default settings for that filter will be restored.
If you want to set your own custom settings to a filter, hold down Ctrl (Mac: Command) as you apply your settings (the cancel button should read “Default” while making all of your adjustments).
After you’ve applied your settings, release the Ctrl/Command key and press OK. Your filter will be applied and the new settings then become the new default settings for that filter.