To activate your installation go to the Settings > License menu in the Web Management Console. If you have no valid license, you will only see your installation's Deployment ID. You will also see a warning in the Web Management Console header.

Settings/License page, when no valid license exists

Press the ACTIVATE button to bring up the Activation menu

Settings/License/ACTIVATE page

If you activated your installation, but your license becomes invalid or expired, you will see a RE-ACTIVATE button. After clicking it, the product tries to activate the license with the formerly entered activation information.