If you are still able to access your account, you can change your email address directly at mypos.com >> Login >> click on the Profile section on the upper right corner of the page >> My details >> You will see the field for Login details >> Edit your email address.
In case you are not able to follow the above steps, you can send us a request at help.uk@mypos.com stating the current email address and the new one you would like to used and we will proceed with the request.