You can use these instructions to change your password in Office 365, please note that this requires your Office 365 Administrator password to perform.
1. Log into your Netregistry domain
2. Manage the domain you want to make changes to
3. Click on Office 365 Email
Find the email address under the Email Accounts section and click Edit
In the Reset Password section enter the Administrator password and hit Next (if you do not have the password you can recover it via the link on this screen as well)
Enter the new password and hit Save