next / previous image?

Hello.

I have many posts, each with one image. When viewing any of my posts I have a grey arrow on the far left and right hand sides of the screen. Clicking them takes me to the next or previous post.
However, on one particular post the grey arrows do not show and instead i now have ‘previous image’ ‘next image’ and ‘return to post’. The ‘return to post’ doesn’t do anything and the ‘previous’ and ‘next’ buttons just take me to a couple of random images from much older posts.
How do I remove the ‘previous image’ ‘next image’ and ‘return to post’links, and just have the grey arrows? I just can’t work it out.

Also, if possible I would like to make the header-background transparent, so that my tiled background image is continuous from the top to bottom of the page.

Thank you very much and a lovely theme.