Create a dbcontext
first
then
CurrencyExchange CurrencyExchangeObject = context.CurrencyExchange
.Where(a => a.Currency = x.ToCurrency)
.FirstOrDefault();
after that you can simple assign the values like
CurrencyExchangeObject.Rate = x.Rate;
CurrencyExchangeObject.DateTimeStamp = Convert.ToDateTime(x.TimeStamp);
and then simply say
context.SaveChanges();