Welcome to FlyerTalk!

There is a wealth of great info. here, but finding it isn't always the easiest thing to do. The Technical Issues forum has several threads on how to use it as well as rants on how it doesn't work. When searching on such commonly used words as "miles" and "upgrade", sometimes the easiest thing to do is check the forum's FAQ (see the announcement or stickies at the top of most forums).

NWA's forum announcement refers you to the wiki FAQ, where upgrading with miles is discussed, including which fares are upgradable.

The NWA forum announcement also has a link to FT's search primer.