All presets install automatically with the plugins. Since presets are managed by the host, not the plugin GUI, Studio One may not display them even though they are installed.
To fix this, right-click and 'refresh' the plugin in the top right corner of the effects section, which should add the presets.
You can also check the Studio One folder in "Program Files" for Windows or "Applications" for Mac to see if the presets are in there.