I want to use the featured image funcion, but I only see the pictures when I have two columns en not just one. And I would like to change size and posiion. Is that possible?

can you explain a bit more - what two columns vrs one are you talking about?
Do you have an example url showing the issue?

Well I saw that I can see the images, but I like to know if it's possible to change the size or place it somewhere else on a page

wait, think I found it! stupid me...

I see post thumbnails, but I want to know if I can place them somewhere else

You can...but you will have to edit theme code to do it - bfa_post_parts.php