Android : Android Google Maps Increase/decreas radius after adding

Right now this is my code for my Android App. It adds a marker on the Google Maps when Long Click, then when you click on the marker it creates a circle marker and removes the normal marker. However I want to adjust the radius of the circle when I add it. Like incrase or decrease it when I move my finger up or down.

    mMap.setOnMapLongClickListener(new OnMapLongClickListener() {

        @Override
        public void onMapLongClick(LatLng latLng) {

            MarkerOptions Marker = new MarkerOptions().position(latLng);

            mMap.animateCamera(CameraUpdateFactory.newLatLng(latLng));

            mMap.addMarker(Marker.icon(BitmapDescriptorFactory.fromResource(R.drawable.human)).draggable(true));
        }
    });



    @Override
        public boolean onMarkerClick(final Marker marker) {

            LatLng pos = marker.getPosition();
            marker.remove();
            mMap.addCircle(new CircleOptions()
                    .center(pos)
                    .radius(radius)
                    .strokeColor(0xFFF7941D)
                    .fillColor(0x90F7941D));

            return true;
        }

Sorry, but does anyone know how to or where I can read more about? Thank you very much.