refresh the circle on google map - google-maps

Question

I'm implementing an application in which I have to show google map with circle at the center of the map. I'm able draw a circle on map but after few seconds I've to update the circle's radius. I want to use same instance of map rather than creating new one.
When i create the new circle its overlapping on older circle. I want to remove previously added circle and show new one.
While checking the api I got this method from Circle class which will hide the circle.
myCity.setOptions({visible:false});
but the problem is I don't have access to older circle instance.
Is there any way which will allow me to get maps markers and infoboxes assigned to that map and remove them?
Below is method which will get called interval of few seconds
function mapByCoordinates()
{
var lat=document.getElementById("latValue").value;
var lng=document.getElementById("lngValue").value;
var accuracy = document.getElementById("zoomValue").value;
var zoomVal=getZoomBasedOnAccuracy(accuracy);
var zm = parseInt(zoomVal);
var tempRadius = getRadiusBasedOnAccuracy(accuracy);
var amstr = new google.maps.LatLng(lat,lng);
var mapProp = {
center:amstr,
zoom:zm,
mapTypeId:google.maps.MapTypeId.HYBRID
};
map.setOptions(mapProp);
myCity.setOptions({visible:false});
infobox.close();
myCity = new google.maps.Circle({
center:amstr,
radius:tempRadius
});
marker=new google.maps.Marker({
position:amstr,
});
myCity.setMap(map);
myCity1.setMap(map1);
infobox = new google.maps.InfoWindow({
content:"Welcome to google map",
disableAutoPan:true
});
infobox.open(map,marker);
map.panTo(amstr);
map.setZoom(19);
}
Thanks

Answer 1

We can make the already drawn circle invisible on google maps by using following method
circle.setOptions({visible:false});
and can null the instance of that map.

Answer 2

Try circle.setRadius(radiusvalue)