As mentioned, you can upgrade to higher classes with SWU's (System Wide Upgrade) certificates that some airlines issue to their elite passengers. At four round trips a year, you may or may not fall into the tier necessary to earn these (others can comment on this).

The other way to do upgrades is with miles. There are two ways to do this:
A. Miles only, but from a specific, higher fare class (most US airlines) OR
B. Miles + cash co-pay (AA) I think this is from most fare classes, although they recently made updates to it.

Here's the thing about using the miles, though- you (in most cases) can only use them on the carrier you earned them on to upgrade. So alliances will not help in this situation. In that case, you do want to look at who flies in to where you're going (China is a big country- where are you posted?), what their earning/burning rates are, etc. In this case, you may even want to look at a non-US airline's program. (Others can advise you better on those than I can.)