To unlock a user account or to reset a users password

Search for the relevant user by entering the user name or display name

Open the user record

To see if the users account is locked. Scroll to the "Account Locked" section

If the account is locked, an unlock button will be visible next tot he lock indicator

To unlock the account, click the unlock button.

Optionally the users password can also be reset (this is only applicable if using Forms Authentication)