Increase the featured image size display for single posts.

Hello!

Currently when I upload a featured image for directory post type, on the front end its only outputting a thumbnail size image on a single directory post view, rather than a larger “header” style image.

I like the thumbnail size when I’m listing directory posts but when I go into one the featured image is too small.

How do I increase this display size? Is it a plugin option or do I have to manually do this as other featured images in the active theme look fine.

Cheers,

UpcomingMedia