If you have configured Password write back on your AD Connect server or your users are cloud users, users are enabled to change their corporate password from Office 365 portal. To change the password from Office 365 follow the below steps:
Go to office 365 portal and login with your user account. Once done, push on Settings -> Password.
On Security and privacy push on Password.
On the new windows insert your actual password and the new password twice. Push on Send.
Once donde, you can use the new password where you want, on-premise and cloud.