If you are speaking about changing the user password on the OS, you can log in as that user and simply type 'passwd', after which it will prompt you to input the new password.
If you are speaking about the login to the Webwasher GUI, this can be done under User Management > Administrators > Accounts, then click 'View + Edit Details' for the desired account, then enter the new password in the 'Change Password' section.
Meaning that, if i am user that authenticate to webwasher via local user database. I need to type "passwd" in
the password box to change password ?
This is separate from what I referenced above.
To change a user from the user database it can be done in two ways.
1. Under User Management > User Database, click 'Edit' for the desired user, then change the password in the dialog presented.
2. On the same dialog box you can have the user can change the password themselves if you were to check the box for 'Password must be changed at next login'