To change your password go to the change password page.
To deliver Single-Sign-On (SSO) at the Atos Demo Company the identity management administration is done within MS Active Directory, and passwords are synced towards all connected services. The password change page is from Office 365. So you might need to login to Office 365.
For additional security 2 factor authentication is by default recommended. Atos Demo Company (ADC) offers USB FIDO compatible security keys.