[SOLVED] How to use Posttumbnails in full posts?

I´m using this function today on my theme. How to edit so I can see my tumbnails and my full posts at the same time.

A way to owerride this setting:

"Post Thumbnails are only displayed on multi post pages, which have been set to display 'Only Excerpts'. See menu tab 'Configure Excerpts'"

A really big thnx for some help here....

I start all my post with a picture if I have to make the size to small or edit something on it to fit the first page I use the posttumbnail function to replace it when a user read the full post. But if the picutre is ok from the begining a olny use the basic image insert. So I have big problem here, alot of post to edit if this not working