MongoClient client = new MongoClient("mongodb://xxx.xxx.x.xx:27017");

            var mongServer = client.GetServer();

            var db = mongServer.GetDatabase("db_test");

            var dbclient = db.GetCollection("test");

            FindAndModifyArgs arg=new FindAndModifyArgs();

            arg.Query = Query.EQ("_id", new ObjectId("5a011a0d59f1654cdc377135"));

            arg.Update = Update.Inc("Age", 1L);

            arg.Upsert = true;

            arg.VersionReturned=FindAndModifyDocumentVersion.Modified;

            var result = dbclient.FindAndModify(arg);

            var p = result.ModifiedDocument["Age"].AsInt64;