Here is what Hubpages says about it:
"How do I change my username?
Unfortunately, you can not change your username. If you need to change your username, please abandon your account and create a new one, with another email address. If you choose to do this, please note that you will not be able to transfer your Hubs to the new account.
This answer was found here: http://hubpages.com/faq/#changeusername