Even though PreSonus rigorously beta tests new Studio One versions before release, the general public is a much wider and much more diverse group and end users will almost always find some issues in a new release.
With that in mind, the best approach when updating Studio One is to install it in parallel as outlined below to avoid any possible frustration and to keep the current version installed in the event that you'll need to use it for any reason in the short term.
** This applies to "dot updates" like currently using 4.1 and installing 4.5. New major versions such as currently using 4.x and installing 5.x always install separately. **
Change the install folder path in the installation dialog from ~\PreSonus\Studio One 4 to ~\PreSonus\Studio One 45 (for a 4.5 update as an example) to install it into a new folder. Putting the version number in the folder name also avoids any confusion about which version is in which folder when you go to remove older versions later.
After installing it, go to that new folder and launch Studio One.exe and then right click the running Studio One taskbar icon and Pin to Taskbar to make a taskbar shortcut for it. Or if you already have a taskbar shortcut for the previous version, drag the .exe to the taskbar to make a new shortcut for the new version.
It will always prompt you to overwrite or keep both versions if Studio One is already installed, so choose Keep Both. After installing it, open the /Applications folder and locate the version that you just installed (it will be listed as Studio One 5 or 6 or similar if it's v4, etc, incrementing) and right click it and rename it Studio One 45 or similar so that you'll know what version it is aside from any others listed there. Drag it to the dock to make a new shortcut for it.
** The Studio One application folders on either platform are not very large comparatively speaking so there's no need to be concerned about multiple installations wasting disk space. Once you're comfortable with an updated version, simply delete the application folder / package and any shortcuts for the previous version.**