In case you have forgot your Magento admin password and need to reset it then you can use the forgot password link provided in the login screen or you can directly reset it in the database.

On the “Forgot your password” screen enter admin user email address and click “Retrieve Password” button, an email will be sent with link to reset your password.

In Magento Enterprise Edition a security feature has been implemented which allows you to set the number of failed login attempts after which your account will get locked.

To make these security setting go to  Admin >> System > Configuration, click the Admin tab in the left column, and select the Security section.