How do i make post images show bigger?

Please i need help on this: when i insert an image into post in my simple catch pro and publish, it shows the image same size with the ones on my front page even when i chose full size option in the media edit. i want the image to show full size in my post or as i may chose to edit it. your help on this will be greatly appreciated. my blog is www.fixmeblog.com thanks.