Error message

You can’t change your password here.

Your organization doesn’t allow you to change your password on this site. Please change your password according to the method recommended by your organization, or ask your admin if you need help.

 

Cause

If your administrator has enforced the policy wherein "User cannot change password" in that case the same policy will be applied on O365 once the user is synced with O365.

Resolution

The user has to contact his administrator for a password reset request.

Admin can reset user password using below command.

Set-MsolUserPassword -userPrincipalName user@consoso.com -NewPassword Nula8787

https://msdn.microsoft.com/en-us/library/azure/dn194140.aspx

Additional Info

Password Complexity Policy

When you enable password sync, the password complexity policies configured in the on-premises Active Directory override any complexity policies that may be defined in the cloud for synchronized users. This means any password that is valid in the customer's on-premises Active Directory environment can be used for accessing Azure AD services.

noteNote
Passwords for users that are created directly in the cloud are still subject to password policies as defined in the cloud.