You can do either. 
Though it’s your email address that joins up your community account and your reviews, so as long as you use the same email for both everything should be linked up and visible ‘backstage’.
Next time you submit a review, if you put a different username in it should re-name all the others associated with the email you used. (it doesn’t like spaces, which I don’t think applies in your case, but just so people know - ‘Ian Chimp’ would be ‘Ian C’, whereas ‘Ian_Chimp’ would stay as ‘Ian_Chimp’)
To change your username you can contact Customer Care: