Trade-up means to upgrade or exchange something for a better version. There are many synonyms for the term. One synonym is "upgrading" which is basically trading something for a better version. Another synonym is "switch" which refers to changing one thing for another. "Exchange" is also a good word to use, which refers to giving something to someone in exchange for something else. "Replace" is another synonym, which means to take something away and put something else in its place. Finally, "improve" can also be used as a synonym as it means to make something better than it was previously. Regardless of the synonym used, the term trade-up means to make improvements to something.