Please refer to the Terms of Service agreement regarding user names. From it:
User names: In an online community, user names are the best (and often only) way to distinguish different members from one another. A person's reputation is associated with their user name as the community gets to know them by that name. Therefore, R2R does not allow user name changes except under exceptional circumstances.
If you feel there is an exceptional circumstance, please send a PM to any mod and it will be taken in to further consideration.