I have a flat tire, and need to take the wheel off my JD 110. There's a yellow rubber cap on the wheel hub, and I'm not sure how to get it off - I assume the tire lugs are under the yellow rubber cap, and I'll need to remove them as well?

Grab ahold of the cap and pull, kind of pulling more on one side than the other. Underneath you will find the cotter pin. To install just kind of line it up and push it back on. It helps to use a shop towel for comfort and protection to your hand.