using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.SharePoint.Client;
 
namespace COM
{
    class Program
    {
        static void Main(string[] args)
        {
            // siteURL is the string that contains the site URL 
            string siteUrl = "http://serverName:50000/sites/Testing";   
            // ClientContext object is used to get the context for the SharePoint objects
            ClientContext clientContext = new ClientContext(siteUrl);
            Web web = clientContext.Web;            
            List list = web.Lists.GetByTitle("CustomList");
            Field field = list.Fields.GetByTitle("Calculated");
            FieldCalculated calculatedField = clientContext.CastTo<FieldCalculated>(field);
            calculatedField.Formula = "=UPPER([Title])";
            calculatedField.Update();
            clientContext.ExecuteQuery();           
        }
    }
}