Say you have a Lego house. A fairly complex one, let's say 10000+ pieces. Say you take one piece off and replace it with another. You probably won't notice much of a difference. Any person who didn't make the change themselves probably wouldn't notice any change at all. Do that every day for 100 days. Now, the house you have is slightly different from the original. Do that every day for thousands of days, and the house will be significantly different. Do it for millions, and the house will be unrecognizable. That's how macro-evolution works.