Alter Gmail username

Let me just get this out of the way... I am a first time Druid owner from using Blackberry for years and first time poster after I have searched for my answer. So here is my question:

The Verizon salesman entered my Gmail username while he was initializing the phone. The user name format is FirstLast. I always prefer that my email is entered into what ever email program I use so that way the capitalized letters distinguish the first and last name. Is there a way to alter this without doing a factory reset?

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