[NOTE: Not applicable to users of HistoryGeo.com for Libraries]
Whenever you double-click on a Custom Marker with the left mouse button, the Marker Details window will popup. If it's a marker that was submitted from your account, then you will see three buttons near the top right of the window. These allow you to Delete, Move, or Edit the current marker.
Deleting the Marker
Whenever you click the "Delete" button, you will be asked if you're sure you want to delete the current marker.
If you click "Yes," the Marker Details window will close, and the marker will removed permanently from the map.
Moving the Marker
After clicking the "Move" button, the Marker Display window will close and you will be presented with the following message:
The marker will change from its usual blue color to red. While the marker is colored red, you are able to click and drag it to a new position.
When you're done, press [Enter] on your keyboard. If you've made a mistake, and want to return the marker to its original position, press the [Esc] key.
After pressing either [Enter] or [Esc], the Marker Details window will reopen.
Editing the Marker
If you press the "Edit" button, the Add/Edit Marker window will open with all the marker's information already filled out. From here, you can change any aspect of the marker's information. (click here to learn more about the Add/Edit Marker window)
After you're done making changes, click the "Save" button. If you don't want to make any changes, click the "Cancel" button.