Pinboard postboxes and margins (padding)

Hello,
I hope that someone can help me with a couple of things that I need to fix to my site. The site is http://www.photosbyhaglund.sehttp://www.photosbyhaglund.se

I am using Pinboard 4.2.4, using 4 columns post on startpage (3 columns and 1 sidebar)

The things I want to have help with is:
1) How do I adjust the size (height) of the postboxes? There is lot of white space under the text.
2)How do I change the margins(padding) so that there is less space between the post? I want to have bigger (wider) images on the posts, how do I do that?

Thanks!
Matte, PhotosByHaglund.se