In the User Account Module find the the user account you wish to modify and click the corresponding pencil icon to update the user account. On the "Edit a User Account" page, you can change the details of the user's profile.
A setting worth pointing out is the status indicator for the user account. This will allow you to disable a user account, therefor preventing them from logging in to the system. This differs from deleting a user account, since deleting a user account permanently erases all data related to the account. Where as setting the status to "inactive" disables the account from logging in while preserving the data.