To edit user credentials, go to Admin-->Security-->User Accounts and click on edit (see gestione utenti).
This will show the screen in the figure below:
In this screen you can edit or delete users, prevent him from login or force user to change password.
In the following screen you can see how to restore locked users after the wrong password several times (Locked Out) using the unlocking button:
Please note that due to the presence of a cache, you may have to wait several minutes before you see the changes in Locked Out.