You need to have this image in several dimensions, so the android itself will be charged to raise the best quality depending on the device. Below the required icon sizes:
MDPI - 48px
HDPI - 72px
XHDPI - 96px
XXHDPI - 144px
XXXHDPI - 192px
Then set the location of the image in icon.
private static final LatLng MELBOURNE = new LatLng(-37.813, 144.962);
private Marker melbourne = mMap.addMarker(new MarkerOptions()
.position(MELBOURNE)
.title("Melbourne")
.snippet("Population: 4,137,400")
.icon(BitmapDescriptorFactory.fromResource(R.drawable.arrow)));