If your SonarQube instance has access to the Internet, you can directly install an Edition from the Marketplace menu in the SonarQube UI (Administration > Marketplace).
If you don't have an access the Internet from your SonarQube instance, here are the instructions to manually download and install an Edition;
- Download the Edition corresponding to your version of SonarQube
- Extract the zip file and drop the results in $SONARQUBE_HOME/extensions/plugins
- Stop/start the server
- Set the license in Administration > License Manager page
After the step #4, whatever message you have with a red background, restart SonarQube and your license will be taken into account.