cant copy files - tried the "USB MTP Mode"

just setting up my new Edge 840 and i want to copy an opensource IMG file to it for more topo detail.

I do not seem to be able to copy / paste an img file to the device Garmin folder.

I am using a windows laptop

explorer shows the device, folders and files

i do not see any property details in explorer suggesting the directory is Read Only

what am i missing?

thanks