Hello Mark 

Thanks for posting in the Lucid community! There can only be one account associated with an email address. To delete your free account please navigate to your Account Settings click the User Settings tab to the left and select “Delete Account” at the bottom of the page. You will be prompted to delete your account at this time.

Once your account is closed we will no longer be able to retrieve the documents you have created and saved to our systems. Please download and save any documents you will need before closing your account. Closing your account will also close any Lucidchart Lucidspark Lucidscale or Lucidpress accounts tied to the same email. You can refer to our Help Center for more information about account deletion. Please let me know if you have any additional questions or concerns.

Once you delete that account you will then be able to change your username to that email. You can make this change through your User Settings page. For more information please view this Help Center article.

Please let me know if you have any additional questions or concerns!