"I want the change."
Translation:Tôi muốn sự thay đổi.
In English, I want the change means I want my change in money back from a big bill. Change, as an abstract noun, is noncount, so we wouldn't say "the change". We might say that we want a change, when we want something in our lives to be different, not everything.
FYI, change (the money given back from a big bill) is called tiền dư/thừa ("redundant/excessive money"), tiền thối (dialect, maybe, no idea why it is called so, but "thối" doesn't mean stinky here), tiền trả lại ("given-back money")
Unless of course it's specifying a specific "change" that you and the other person know of, though normally it would be followed by some other words like: "I want the change (that you mentioned) to be realised".