Update the SharePoint List Item using C# Coding

// Open your SPSite
using(SPSite oSite = new SPSite("Your Site Url")) {
    //Get a Root Web
    using(SPWeb oWeb = oSite.RootWeb) {
        //Get a Particular List
        SPList oList = oWeb.Lists["Your List name"];
        // Get the Item ID
        listItemId = 1;
        // Update the List item by ID
        SPListItem itemToUpdate = list.GetItemById(listItemId);
        itemToUpdate["Employee Name"] = "Adam Smith";
        itemToUpdate.Update();
    }
}