How to change size of marker ? (more bigger)

If you want to use bigger markers, then you first have to follow this article how to use custom markers.

Then use this filter to specify the larger size. The $marker_props[‘scaledSize’] value should be half of the original image size, the other values you have to play around with a bit to see what works for your marker.

All code has to go in the functions.php inside your active theme folder.