Hello @support​,
My name is Henry and I am happy to assist with your inquiry, and appreciate you contacting LastPass Support!
I am sorry about the issues you are having trying to change your email. You will need to delete the account under the new email address. You can delete it following the steps on this article. Once deleted, you should be able to change the email on your existing account.
Please let me know if this worked or if further assistance is required.
Thank you,
Henry | Customer Care