T42S phone not allowing to change default admin password?

[SysAdmin-Edgar]

I have yealink phone T42S with firmware version 66.9.0.45 and I’m trying to change default password of admin to my own password.
When I log into phone using web browser I go to Security tab and for User type I select admin and for old password I enter admin.
For new password I enter a new password and for confirm password I re-enter my new password. Then phone automatically boots.
I wait a few minutes and when I try to login it does not accept my new password and I can’t log in. I have to hold ok button to reset
phone to factory settings.

How do you change default password admin to our own password?