Dave Mason shows how to install Reporting Services 2017:
The SSRS 2017 installation media was easy to find and download from Microsoft. When I ran it, the installation process was simple. There were very few choices to make, and none of them were terribly important or impactful. Other than clicking “Next” buttons, the only choices and input required was to choose the SSRS Edition (or enter a product key), check the box to accept license terms, and choose an installation path (if you don’t want the default). It was so easy, it almost feels like a waste of time to post the screen shots. But since I have them, here they are:
Click through for a block of screenshots and more install info. As for Dave’s question as the end, I think the only way you can have two versions of SSRS 2017 on the same instance is if you have Reporting Services and Power BI Report Server, and they’ll show up in Reporting Services Configuration Manager as SSRS and PBIRS, respectively.