When you're creating a new post or in Edit Post mode, you'll notice an A/B button on the top right of your screen. This allows you to test two different titles for any post to find out which one drives more engagement.
This system will randomly show half the visitors to your post the first version, and half the second version.
Click on it and give it a try! You can find the results of your A/B Test when you click into A/B tests.
Activating an A/B Test
You can easily activate a test, by clicking on the icon in the top right when editing a post. Once you've added a second title just click X in the upper left corner of the Title A/B Test sidebar and voila!
Deleting an A/B Test
To cancel or delete the test at any point, simply go to Edit Post, click on the A/B icon, and delete the second title.