You are now able to replace the media on single image posts, videos and pins!
To replace the media on a post:
Edit the post
Select the post you'd like to change the media on from your home calendar and click Edit where you'll be taken back to the quick scheduler.
Click 'Upload Media'
Click Upload media and you can either drag and drop an image or choose a file from your computer to upload.
Save Changes
Scroll down and click Save changes. You will have officially replaced the media for that post!