Google is showing my old URL, how to remove that from google index and index new one

Recently I have made changes to my URL I have changed http://letsfindcourse.com/machine_learning to this http://letsfindcourse.com/machine-learning but google is showing my old url in google search. I have already submitted new sitemap to google 2 days back. But still it is showing old url. Can someone help me how to solve this issue ?