Clean Blog Theme picture problem

Hi there – hope Im not repeating anything , Im new to this…

Ive installed the theme fine and its works great but when I try to add an image – it doesnt show up, Ive creted the correct size gif .gif image (570×310 pixels ) file and uploaded it (added it under media and add new. I’ve attached it to my first post (the heading of the post is showing up in the bottom of the slider) but its not showing up on the site. Would you have any idea!? Thank you in advance.
ps, Have tried to attach other pics and they attach ok but dont appear on the site?.

Im not sure if Ive given enough of info here – maybe I’ll need to give the website name to help further?.