Ok. You have less than a day. You have waited until it is very late. At this point you have a few options and none of them are good.

1. Try to piece something together very quickly. I know of preachers who read a text superficially and then put together a sermon that was "decent" in an hour. Sometimes even a truly great sermon can come together at the last minute, but often it does not. I would encourage you to look at our Last Minute Preacher's Guide for an approach to doing this. Keep in mind, however, that this is not the idea.
2. Copy a sermon. Replace the illustrations or add illustrations from your own life. If you want to do this, I would suggest the following procedure. First, read the sermon, mark the stories and note their purpose. Then look in your life for stories that could serve the purpose of each story that is already in the sermon. Replace each story with your story. Then, practice the sermon.
3. Copy a sermon verbatim and give credit to the original author. I would suggest that if you do this you follow two rules. First you let the people know that you are using someone else's sermon. One preacher had a very ingenious way of doing this. He told the people that it was a "Christian History Sunday." Then the preacher simply read one of the sermons from history. You can find someone like Charles Spurgeon's or John Wesley's sermons on line. Then simply preach it. Another preacher said something like: "I read this very helpful sermon and thought it would be helpful to you." One should recognize that one cannot do this often or the people will not go along with it, and rightly so.
4. Copy a sermon verbatim and do not give credit. This is the most common approach as well as the worst possible approach. This is problematic in that it is the least honest method. It is problematic because it attacks your creativity. And it is problematic because people have lost their job doing this. It is put here simply for completeness, but DO NOT TAKE THIS OPTION.

Preachers are paid to give a word that God has given to them. In addition, God has called them to give a message. To simply copy a message is wrong for many reasons. However there are times when our back is against the wall and we need to give a message and we did not spend as much time as we should have spent in preparation. In those very few cases, let us ask God for forgiveness and make the best of the situation. In addition, I would encourage preachers who find this happening too many times to make use of your assistants. Letting an assistant preach more often can take some of the pressure off of the preaching pastor to be creative. And on top of it all, that is why they are there, to assist the preaching pastor.