To delete stored user names and passwords

To open User Accounts, click Start, click Control Panel, and then click User Accounts. If your computer is joined to a domain, click the Advanced tab, then click Manage Passwords. If your computer is not joined to a domain, click your account name and then, in Related Tasks box, click Manage my network passwords.

You must be logged on as a computer administrator to complete this procedure. 

View and modify stored user names and passwords

Store a new user name and password