Once a User account is created, it can be modified two ways. One method is through the login form on the site, if it is being displayed. The other method method is through online administration.
After a user logs in through the login page on your site, they will see a Settings link. That link will take the user to a form that is similar to the form used for creating a new account. They can use this form to update their information and change their password.
To modify a user through online administration:
Click Users under User Accounts in the administration menu.
The following page will display the list of users.
Click the Edit link next to the user you wish to modify
The following page will appear similar to the page for adding a new user. You will not be able to change the username.
Click the Save button at the bottom of the page when you have finished making any changes.