To access the library, please open Finder, and then select the 'Go' tab along the top toolbar. Hold the option key to reveal the library in the list of locations.
C:\ProgramData\Akai\MPC\Expansions
If you are unable to view the Program Data folder within the Windows File Explorer, you will need to enable 'show hidden items'. To do this, please select the 'view' tab in the File Explorer, and tick the box that says 'hidden items' in the show/hide section.