Configuring the Default Settings
The tinyMCE module contains a number of predefined settings: e.g. which options (bold, italic, underline etc.) appear in the rich-text toolbar, whether the toolbar appears at the top or bottom of the field, and so on.
To configure these settings, go to Modules -> TinyMCE Field Type. There, just construct the default rich-text editor that you desire. You’ll note that changing the options automatically redraws the example editor below. This keeps the settings completely transparent so you’re never unclear about what it will look like.
Note: these just specify the default settings. So when you choose this field type for any of your form fields, it will inherit all those values. However, every field type can override any of these fields.