Hi Jo Ann,
A few times we've booked a "guarantee" cabin in hopes for an upgrade. When doing this though, you need to book the least catagory cabin you'd want, in case thats what you get. Always talk to your travel agent and see if you can book that way, unless you want a specific cabin, then book it that way.
Here is a link to an article that explains booking a "guarantee" catagory cabin:
Here is one that gives some information on getting an upgrade: