I saw you guys talking about upgrade here. I would like to ask a quick question. I am so new that I have never used miles to upgrade and I don't understand much about fare class. Typically, I buy whichever the cheapest available. Because of that reason, now I have 24K with DL, 22K with UA and 21K with AA; 14K miles to come in Korean Air. (I know it's bad!)

To ask you guys a question, let me use an example of UA. I am looking at United award upgrade chart, which says "Upgrade - Select United Business (C and D) to United First, or select United Economy (M, H, Q, V, W, S, K, L, T) to the next class of service... from North America to destination within North America 15K miles".

If I have a UA tix class S or T (which I got for my recent trip to Hawaii), does it mean that I can redeem 15K miles to upgrade all 4 legs to business class (IAD-LAX:LAX-HNL .. HNL-SEA:SEA-IAD)? Is it that simple? Is there any fee or limited availability? Thanks in advance !