You are not allowed to change your user name. I am not sure you can delete the account. The best thing you can do is not to use it. If you want to change your username, you could probably transfer your hubs, but not the comments, q&a, etc.
You can change your hub photo (picture) that shows on all Hubs, questions, etc.
You can do that by editing your profile page. When you go in the edit mode, go to the bottom and make the change.
You may be able to delete the account or just do not use it. I have a second account that I have never used.