Trouble launching RStudio v 1.1.456

Hi, I've just installed RStudio v 1.1.456. Why does it say that I have to close it before installing a new version? It's the only one I have! I just installed R v 3.5.1 a couple of minutes prior.

Are you sure you're opening RStudio from your computer and not the installer or disk image?

On a Mac, when you download RStudio you get an installer, which creates a disk image:

When you open the disk image, it looks like this:

This is telling you to put RStudio in Applications (which you can do through the folder alias inside that window). To run RStudio, you then open it from your applications.