Hello Namita,
instead of a JSON Model (which is more for client side models) you should use an OData Model for the consumption of your OData service. You can use sap.ui.model.odata.ODataModel or the newer version sap.ui.model.odata.v2.ODataModel if you have an up to date UI5 version.
The OData Models have an "update" method which allows you to update a record set.
In the SHINEs UserCRUD application you can find an example for the "create" method (cloud-hana-shine-sp8/userCRUD.controller.js at master · SAP/cloud-hana-shine · GitHub). Using the "update" method is pretty much the same. The coding should give you a first insight in doing the things.
Regards, Florian