hello 兌 is a rare word in modern Chinese, we wouldn't use it alone, and we often combine it with other words, and it's often involved in money here 兌and 換 are the same meaning, means exchange or replacement, and when we put it together, it is to emphasize that you have a "right" to exchange , especially when you hold a paper, ticket , coupon, check in your hand. Sometimes it implies that you can exchange it for better things or other things. e.g. when you go to a shop, talk to the clerk 我要兌換獎品 it means you've possessed a thing and you want to exchange it for the gift. What you've possessed may be a ticket, coupon or paper and when you say 我要換獎品 it means you've got the gift and you want to exchange a new one and when you go to the bank 我要兌換支票 it means you've had a check and you want to exchange it for cash 我要換支票 it means you've had a check and you want to exchange for a new check