By pressing F11 you can toggle between full screen and normal mode. However this functionality is no available in the Lite version of the RadEditor.
Regarding the Width, you can control it only in Web Part or WCM scenario, not in list (list, wiki, blog ...) scenario. In order to do so you need to modify the respective ConfigFile.xml, which is located in the Program Files/Common Files/Microsoft Shared/web server extensions/wpresources/RadEditorSharePoint/4.x.x.x__1f131a624888eeed/RadControls/Editor
folder. Add the following code:
or define the with in pixels.
I hope this helps.
the Telerik team