Go to “Edit Theme” section, and disable the “Use caption” option to remove a post caption. Notice that some themes display image navigations instead when you disable the 'Use caption' option. If you are not familiar with how you open up your customize page, you may want to take a look at our article (Where's my customize page?)
'Use caption' is a built-in option on all our themes. Enabling this option simply creates a post description on your blog posts, and vice versa. This is a different approach from the 'Hide option'. The 'Hide option' hides your captions only, leaving the post controls such as the like, reblog, post notes, or share on some themes.
We recommend to keep your captions for your search engine optimization (SEO), though!
Have any questions? Feel free to leave a comment here!