Removing Space around header position on Articles.

Hi I would like a bit of help removing space around the header position on articles. I should be able to work this out myself.. but oh well.

Take a look here:
http://cms.molinosmodo.com/index.php/en/molinos-de-cafe/molinos-de-cafe-hosteleria/3-molino-dh

You can see an image in the Header position (it's simply an html module).

Can you answer the following questions:

1) Is an image in an html module the best practice for displaying an image like this at the top of an article (it will be different for ever article)?

2) What is the ideal size this image should be?

3) How do I make it so it fills the whole header space (responsive) like this page?:
http://demo.gavick.com/joomla25/photo/index.php/blog/single-article

Thanks in advance.

In our demo server we use k2 articles which allows to select article image - it is used to fill the space correctly.
If it goes to image size - it is alway stretched to fill the entire browser window, but you need to chose size and compression wisely, specially when your users uses mobile devices as big images will load slower.

Thank you for the unswer - that helped me also.
Is it possible to change the hight of the picture? We need to scale it to max. 200px.

Thank you & greets.

Please post a link to a page where an image is added correctly.