Picture Posting

[Johnny Reefer]

I tried posting a few pics in a forum thread for the first time. I could not seem to figure out how to post anything larger than a thumbnail size picture.
I am following the instructions laid out in "How to post pics" to a tee. (At least, I'm pretty sure I am). I would like to post pics larger than thumbnail size.
What am I missing here, please?

Thanx much,