Serum 2 (and Serum 1, as the process is identical).
Select "Add Folder to Favorites..." and navigate to the folder where you unzipped your new presets. how to install serum 2 presets
Installing presets for Serum 2 is straightforward, but there are two main methods: (full control) and the Preferred Method (using the built-in preset browser). I strongly recommend the second method. Method 1: The Preferred & Easiest Method (Using the Serum Presets Folder) This method keeps all your presets organized inside Serum’s own directory, making them appear automatically in the plugin’s browser. Serum 2 (and Serum 1, as the process is identical)
Go up one level (or simply remember the location). You don't need to put presets inside Serum’s folder for this method. I strongly recommend the second method
Unzip the preset pack you downloaded.
In Serum’s browser (left side), click the "File" menu at the very top of the browser panel.