Outlook Web Access (OWA) built in to the Exchange 2007 server shows a "change password" button in the options pane when a user is logged in. It is enabled by default, even if the password change functionality is disabled by default - frightfully clever from Microsoft...

Anyway, it's a small thing to enable it (source: Knowledgebase Article 297121):

1. Click Start, point to Programs, point to Administrative Tools, and then click Internet Services Manager.
2. Right-click the default Web site, point to New, and then click Virtual Directory.
3. In the Virtual Directory Creation wizard, type IISADMPWD in the Alias box, and then click Next.
4. In the Directory box, type c:\WINDOWS\system32\inetsrv\iisadmpwd or the location where your hard disk is your default hard disk, and then click Next.
5. Verify that only the Read and Run script check boxes are selected, such as the ASP check box, click Next, and then click Finish.
6. Verify that the IISADMPWD virtual directory has only basic authentication set .
Click Tab Directory Security and give a checked on basic authentication.

Try to login into OWA. Ex : https://wowtutorial.org/owa
Click Options menu and find any Change Password
Input your Old Password
Input your new password
Re-Input your new password again
Log Out from OWA

Clear your browser cache and try to login into OWA again with your new password.
If you new password is working that your success :)