The application administrator within your organisation can change email addresses for all users. if you do not see the 'Users' option in the 'Settings' menu your user does not have the correct authorisations. Use this guide to change your own email address.
Go to the Campaign Manager and log in with your credentials.
Select 'Settings'.
Click on 'Users'.
A pop-up is shown for SMS authentication.
Search for the user whose email address you want to reset.
Select the user.
Fill in a new email address
Click on 'Save'.
The user now has a new email address registered to their account.