Studio One 4 comes as a 64-bit program only. There is not a 32-bit installer for Windows, and you cannot run the program as a 32-bit program on a Mac.
That being said, if you have 32-bit plug-ins that you need to load inside of a 64-bit host, such as Studio One 4, we have two suggestions. Please keep in mind that your experience with any of these 3rd-party programs can vary from one plug-in manufacturer to another. PreSonus has not tested the use of these programs with all 32-bit plug-ins inside of Studio One 4.
1. There is a program called jBridge that allows you to wrap your 32-bit plug-ins, so that they can run in a 64-bit host. jBridge has a Windows and Mac version of the program. Here is a link to the jBridge web site. https://jstuff.wordpress.com/jbridge/
2. There is another program called 32 Lives that was developed by a company named SoundRadix. 32 Lives will allow you to wrap 32-bit Audio Units as well as VSTs, so that they can run in a 64-bit host. This program is currently Mac-only.
Here is a link: https://www.soundradix.com/products/32-lives/
For support with either of these products, you will want to contact their respective manufacturers.