Oh deary me, you must have been naughty!
Unfortunately, short of hacking your character there is little you can do to reverse this.
Rangers and Paladins are 'heroic' classes which are very much intended to be played in a certain way, and the fallen status reflects that you have let your reputation drop too low. View it as a punishment for not behaving in the way a ranger should. You can either go back to a previous saved game and keep your reputation higher, or relish your fallen status and play through the rest of the game as a twisted, bitter bad-guy - a viable role-playing option! - Your choice.
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Time is an illusion. Lunchtime doubly so.
Epona of The Laughing Hyenas and The Ladies Guild.