When you'd like to change the email address you're using for Metatask, please go to the account drop down menu and choose "Profile Settings" from the drop-down list.
On tab "General settings" enter your new address and click "Save changes".
You will then receive a verification email to your new address. Please click button "Confirm your email address" to verify and start using your new address.
Please remember that until you verify your new email address, Metatask is unable to send you any email notifications.