Notewise Cloud does not currently support changing the email address associated with your account. The email address you used to sign up for Notewise Cloud is the one that will remain associated with your account.
If you need to use a different email address, you will need to create a new Notewise Cloud account with the desired email address. However, you may export all your notes from your current account as .notewise format and then re-import them to the new account. This will allow you to maintain your existing notes and data.