To add delete or change password for a user just goto dashboard and type user account and press enter. In the user window unlock the username you want to edit by click on the lock button on the top and then make changes you want.
To add new user
Open the terminal and type in the following command sudo adduser username Here replace the keyword username with the new user, that you want to add. You will next be asked password for authorization , password for the new user you have just added and some basic details. After entering them click on Y for confirm and new user will be added. Check out the following snapshot for example.
To remove existing user
sudo deluser username
To Change user password of current user type passwd To change password of any other user type passwd username Replace username with the name of the user whom you want to change the password.