How do I remove the grey box around the images on my homepage?

Hi,

I am reasonably new to WordPress, and can do basic things, but not very good at the CSS stuff.

I’m adding adverts to the sidebars of my WordPress site, but they are coming up with a grey box around them.

The image doesn’t sit very neatly in the box and always seems to sit to one side instead of in the middle.

I am using Magazine Basic theme.

Link to my site is: http://www.vandoak.com

How can I upload images that just sit neatly beneath each other in the sidebar like on most other website?

I have asked a friend who’s into coding. He has changed the code in the style sheet but it hasn’t made a difference. Apart from the ‘Update File’ button, is there anything else he should press to make the changes come up?

Any help would really be appreciated. I have been trying to fix this for ages.

Thanks in advance,

Ana