Presets for FabFilter One are stored in separate files with the .ffp extension (for FabFilter Preset). All presets reside in subfolders in the main preset folder. The subfolders will show up as separate categories in the preset menu. You can also further divide the subfolders into categories, for example to create a Drums > Hihats category.
You can move, copy, rename and delete the preset files just like other files. The easiest way to do this is in the Save dialog that appears if you are saving a preset. The preset menu will automatically reload itself with the changes when the dialog is closed.
The default location of the main preset folder is My Documents\FabFilter\One for Windows, and ~/Library/Audio/Presets/FabFilter/FabFilter One/ for OS X. To change this location, first copy all presets to the desired new location, and then click Change Preset Folder in the preset menu to select the new folder.
Because FabFilter presets use the same file format on Windows and Mac OS X, you can easily share your newly created presets with other users.
See Also
Saving presets
Using FabFilter One