How to redsign the comment box?

I would like make the comment box all over the column, 640 px. It is now 350. I dont find any tools for doing that.
Do I have to edit some css-files?

It looks like you are adding the comment box via the content plugin and its default is 350px. To modify the width, you will need to update the setting in the JFBConnect > Social > Content Plugin - Comments tab.

I also would like to place the box underneath the "Read more" link. Now you miss the Read more.

As a content plugin, we only have the ability to place the comment box above or below the text. The readmore is not included in anything that JFBConnect sees when adding the social code. To do any more specific positioning, you will have to do a template override of the article view to insert the read more at a different location.

-Melissa

Here are a few quick suggestions:
1. Please make sure you're using the correct tab for comments based on what you're using to display content. There are two tabs - one for K2 and one for Joomla and it's easy to set the value in the wrong one.
2. After setting the width higher in the JFBConnect > Social area, please try to clear your cache to see if this helps.
3. Try setting the value to 100%.

Let me know if any of these help.

-Melissa

No problem. I've made the mistake myself, which is why I mentioned it. Glad it was a simple fix.