You can definitely change the email address that you signed up with on FlexClip. However, you can not do it by yourself at present.
Please contact our customer service team at support#flexclip.com (replace # with @) and provide the new email address using your old email address. It should be noted that the new email address cannot be a registered account.
After confirming that you are the account owner, we will help change your account ASAP.