Dee, most of the staff at TACA probably speak English, (I love that airline), but if not, you can ask "Tienen ustedes asientos en primera clase?" (do you have any seats in first class?)
I have had pretty good luck with that. I always ask if there are upgrades available when I check in. Sometimes, they give me one, gratis. Sometimes, they say "Sure. It'll be $40". Most of the time, though, they either say no, (especially of the flight is not full), or that it would cost me a gajillion dollars. Once, I was gabbing with a flight attendant before I got on the plane, and after we took off, she poked her head through the curtain and pointed at me, and gestured for me to come up. She handed me a glass of champagne and a menu. :mean: That was a rare case, but it's always a good policy to be nice to people.
To increase your chances, arrive at the gate early. They like it when you do that. I have been handed the most free upgrades that way, including the last flight I took home from Europe last month, that was awesome!