Here's what I did. First you have to change the email address of the user you want to change to one of your personal email addresses, one not linked to dropbox. Then log out and sign in with that personal email address of yours but click the forgot password link. Go to that email and reset the password. Then log in as user using your email and new password. Click the smiley face and under settings change the name. Then log out and log in as admin, change the email address to the user's email. Reset password. Should be much easier.
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