Click on Files as shown in the following screenshot:
Click on Business Intelligence Server.
There are several versions available to be downloaded (as shown in the following screenshot). Choose the latest stable version. At the time of writing, the latest stable version was 4.8.0.
If you are using Windows, choose biserver-ce-4.8.0-stable.zip. But if you are using UNIX or Linux, you should choose the biserver-ce-4.8.0-stable.tar.gz file.
Extract the file into a location of your choosing, for example, C:Pentaho. You will have two extracted folders, biserver-ce and administration-console. We will refer to the folders by [BISERVER] and [PAC] respectively.