Instructions for Mac OSX users:

    Make sure Garmin Basecamp is installed and closed; Also MapInstall and MapManager for the Mac must be installed.
    Unpack the zip file.
    Double-click on the OFM(EU2024x).gmap folder to run Garmins Mapmanager or
    start Garmin Mapmanager and find the OFM(EU2024_x).gmap folder
     to install it

Instructions for Windows users

    Unpack zip file and move the  OFM(EU2024_x).gmap folder to the default Garmin map folder. The location of this default folder depends on the Windows version. 
    C:\ProgramData\GARMIN\Maps or
    C:\Users\{user}\AppData\Roaming\GARMIN\Maps (hidden folder!) or

You can also put the map on another folder or drive, make a shortcut and place that shortcut in one of the folders above.
Uninstall the old version first (remove the gmap) or by uninstalling it if it is installed on the old way with the setup.exe in the windows register. An easier way to install the map is with Javawa GMTK: https://www.javawa.nl/gmtk.html