Originally Posted by
moondog
1. Make sure the fare class is upgradeable
2. If there is also upgrade inventory available at the time of booking, you can fork over miles for the upgrade at the same time (in the case of CX, at least)
Obviously, make sure you have suitable upgrade instruments handy before committing to #1 because upgradeable fares are often substantially more expensive than the lowest available fares.
By fiddling around the options on that page.. was able to see some changes to booking code. Got the idea. Thanks @moondog