Sending Luggage by Train

I'm a tourist in China (with only a hotel address in Kunming) and would like to send my luggage (mostly gifts) from Kunming to Xining by land while I fly to Xining after spending one week in Kunming. I plan to send the luggage soon after arrival from North America, so that it will arrive at by friends home in Xining when I go there. Could you recommend the best way to do that.