how to zoom in and zoom out map marker

how to zoom in and zoom out map marker

var marker = new google.maps.Marker({
position: location,
id: obj.POI[i].Poi_Id,
html: 'Poi_Id: ' + obj.POI[i].Poi_Id + '<br>Org_ID: '
+ obj.POI[i].Org_ID + '<br>Parent_ID: ' + obj.POI[i].Parent_ID
+ '<br>English_Name: ' + obj.POI[i].English_Name +
'<br>ShortEnglish_Name: '
+ obj.POI[i].ShortEnglish_Name + '<br>Arabic_Name: ' +
obj.POI[i].Arabic_Name
+ '<br>ShortArabic_Name: ' + obj.POI[i].ShortArabic_Name +
'<br>Govt_Telephone: '
+ obj.POI[i].Govt_Telephone + '<br>Govt_Email_Address: ' +
obj.POI[i].Govt_Email_Address
+ '<br>Govt_Fax: ' + obj.POI[i].Govt_Fax + '<br>Govt_WebSite: ' +
obj.POI[i].Govt_WebSite
+ '<br>City_ID: ' + obj.POI[i].City_ID + '<br>Latitude: ' +
obj.POI[i].Latitude
+ '<br>Longitude: ' + obj.POI[i].Longitude,
map: map
});