Garmin hcx os maps

[goldeneagle1]

Does anyone know how to get os maps onto garmin hcx. It's a gps for use in hiking,biking etc. On the well known auction site some sellers are selling a full GB map on micro sd card but it's not an os map & doesn't have the same detail. Ideally a jailbreak for os map software ( memory maps) . I have the original software for GB national parks but I'm struggling to register the software, might be a Windows 10 problem. I would like coverage of all GB ,so any walk can be tracked. I welcome any advice on adding maps even if they aren't os maps.