By Abhinav Parmar and Lisa Baertlein (Reuters) -United Parcel Service posted better-than-expected results on Tuesday, in an early positive sign of the company's overhaul following several difficult quarters of weak volumes. Shares of the company rose 12.1% in premarket trading, with rival FedEx also gaining 3.2%. UPS shares are down about 28% since the start of the year. The profit beat and the forecast signal progress in UPS' efforts to rebuild margins and stabilize volumes after a bruising year marked ...