This section was provided by my friend Peter Mill, who was finding that his Mac was not well catered-for by GPS software.
He managed to track down the answers he wanted and it seems useful to quote them here.
(A link to the original information is also given)
It is also useful to upload the KML file to "Google Maps" to give someone a copy. Sign in to Google Account and the choose My maps and create new map by uploading the KML file created in GPS Visualizer.
Everything above was learned through visiting: www.tommangan.net
If waypoints need to be edited on the Extrex H, the website www.streetmap.co.uk is useful for any UK walks. The "Move Arrow" feature allows you to pinpoint the exact coordinates. Use the "Click Here to Convert Coordinates" feature to obtain the units that will match those selected for your Extrex H. Also right click in Google Maps and use "What’s Here" and use mouse pointer over inserted mark.
Format for Google Earth Searches
Enter Garmin waypoint locations as in the following example: 53 11.546N, 001 41.823W for Lathkil Hotel in Over Haddon. [SK205644 on Ordnance Survey Grid]