I think your friend has to call United with your record locator or perhaps PNR and tell them he wants to upgrade you using his miles. He may have to have status to do this; I'm not sure. I have a family member who is 1k and has done this with me in the past. You can surely get more answers on the United Forum. But be sure to keep your AP number in there since it reflects your *G status and will push you up on the upgrade list.