trellotrello-labels
It seems it's possible to change label's name, but I can't figure out how.
I found the label list in the board preferences, but the names aren't editable, they turn from grey to black when my mouse comes over, but that's all.
How can I change those labels' names?
As of November 21 2014, Trello allows you to add unlimited labels:
http://blog.trello.com/introducing-unlimited-labels/
One way to easily transfer labels from one board to another, is to create a dummy card, assign all available labels to it and then move it to the new board. In this way only the default unnamed labels have to be removed.
Best Answer
It seems that you don't have the permission to change them.
Try to take a look at the ownership of the board, you should be a co-owner or the creator to be able to have them changed.