I have very little knowledge about upgrades to business class, so I am asking for you advise.
Situation: my company is paying for economy tickets East Coast to Sydney, Australia for three of us next year (May 2014). I would love to be able to upgrade economy to business using miles. As of now one of us has 15,000 US Airways miles, 15,000 United and about 70,000 UR. We are willing to help ourselves via CC sign ups, and I guess we should start plan now to have right status and number of miles by next yer.

Would you please explain how upgrades work and what should be our strategy?
Since we don't know what airline we will use, I assume it will be star alliance, it usually more or less the cheapest option.