Members: Manage Locked Members

You can view members that have been locked due to a number of failed login attempts from Admin CP --> Members --> Manage Locked Members.
You can unlock, ban or delete any of the listed accounts by selecting the checkboxes and using the tool at the bottom of the list.

To manage the settings regarding account locking, go to Admin CP --> System --> System Settings --> Security & Privacy and scroll down to the "Brute-force Account Locking" section.