We do not currently have a way to change usernames, and we ask that you only have one operating account if you are not a plugin or theme developer: https://www.ads-software.com/support/guidelines/#do-not-create-multiple-accounts-sockpuppets
If you’d like to create a second account to have a different username, and you are not a plugin or theme developer, we can essentially facilitate a name change by deactivating the account of your choice. Just let us know. (If you do create a second account, are not a plugin or theme developer, and don’t let us know, we’ll just deactivate the first one we come across.)