All versions of Robot Manager are Pega applications with no direct executables. As long as you have the correct version of the platform (7.3.1 for v4) you can directly install Robot Manager without installing previous versions.
Robot Manager is an application you install inside your Pega Platform (or a new instance of it). When used, it becomes a trigger mechanism and the sole provider of data and work for the robots. It has no effect on which automations you can and cannot use. The PDN has many articles and instructions surrounding Robot Manager.