To change the name of a Board you need to go to the Dashboard.

Find the Board that you wish to change its name and click on the preview or name. This will enlarge the preview to twice the size.

Click on the Name/Title under the Board preview and it will become editable.

Change the name and hit enter. That's it, your Board has a new name!

Under the Board name are links to Delete the Board and Invite guest users, this is a convenient way of adding users without opening the Board.