There is an Admin Tools button in the upper left corner of each Brandboard, where you'll find your admin tools for that Brandboard. Visitors and collaborators will not see that button.  The tools in the menu are:

Manage This Brandboard

Brandboard Properties: Where you can change the Brandboard name, status and other page settings.

Collaborate (Invite and Manage): Where you can view current collaborators and add new ones (just click the +).

Brandboard Previews

See Collaborator View: Where you can preview what your collaborators will see when they access your Brandboard.
See Public View: When you've set your Brandboard to "public," this will allow you to preview what public viewers would see.

Add Library Content

Clipps Library: Where you can choose from Clipps added to other Brandboards, to quickly copy them to this Brandboard.
Brand & Links Content Library: Where you can choose from links, email, images and other content added to the Brand & Links Column on other boards, to quickly add them to this Brandboard.

Brand & Links Column

Add/Manage Logo: Where you can add or change the image that will appear at the top of the left Brand & Links Column.

Add/Manage Tagline or Title: Where you can add or edit the text that will appear above that image.
Add/Manage Links & Images: Where you can add and manage the links, emails, images, headers and more that will appear in the left column.

Watch this video about creating your first Brandboard, including details about the Admin Tools menu.