You cannot delete old or duplicate user profiles. Instead, enter your ORCID in all of your profiles (What is an ORCID? and How do I add an ORCID to my JMIR User Profile?). In other words, you need to login to all your user accounts one by one and make sure you add your ORCID. This will lead to a virtual merge of submitted manuscripts and review requests (which will now show up on all accounts), and any Karma points (if applicable) will be credited to the same user, identified by a unique ORCID.
See also:
For staff: (for staff) User delete requests