If that's the email address on your roku account, you should be able to log in and change that one.
If they also have another email address for you, then I don't know about that one. (I've never used Roku as a direct retailer so I don't know if store accounts are the same or different from roku player accounts.)
Is there a way to talk to a human at Roku? The serial number on my account has the first few numbers changed from what my actual serial number is. The website has a spot to type in a serial number not linked to my account, but it won't let you proceed once you pick that option. I was just looking for a way to talk to a human from Roku.