In order to manage your Labels, please check the left navigation bar and click on Labels (under User Administration).
You will find a table with all your Labels and a description of each one. To modify the name of a particular label you need to click on it, change its name and hit enter key. This will take immediate effect throughout the Dashboard.
You can also add comments to every label by click in the Description row, entering your comment and hitting enter key. This is useful to add some annotations that will be seen by every user with access to the Label Administration section.