You can use labels to rename many titles on the board (e.g. new post, reply, who's on line, etc...). Labels are especially useful when you have a board on which the language is not English. They can also come in handy on April Fool's day :)
All admin actions require that you are signed in with an account that has admin access to the community you wish to manage.
The admin dashboard of your community can be accessed by clicking the "admin" link in the community's navigation bar.
Click Manage Forums in the dashboard's sidebar:
Be sure to check the box by Use Custom Labels or they won't show up.
The list is sorted by the various areas of the board. You can change one field or all of the fields.
Once you have finished, scroll down and click on Submit.