Installing the Community theme is pretty easy! All you need to do is follow the steps below:
From your WordPress Dashboard, go to Appearance > Themes and click on Add New.
Click upload Theme – upload your CommunityTheme zip file
Install and Activate it.
It is shown in the image below:
If you missed activating the theme or somehow deactivated Community, you activate it manually with the following steps:
Go to Appearance > Themes in the WordPress Dashboard.
Now, hover over the Community theme thumbnail and click on the Activate button.
Additional information: WordPress Codex – Using Themes