The stockist map is populated by the Google sheet. So if you remove or add stockists on the sheet, this will update on the site automatically.
You may need to refresh the page to see the new updates.
Make sure to include the longitude and latitude for any new locations.
To add these in, you need to:
Ensure the full address is in 1 column
Then use a Google app called GeoCode.
Once installed, you'll find GeoCode in 'Extensions'. Select the column with the address, then go to Extensions > GeoCode > Start GeoCoding