[Theme: Oxygen]: Remove right sidebar, and extend content to fill space

I know this is a problem many people have, and i have read a lot of other posts on this problem, but i can’t get my content to work properly.

http://livesnowriders.com

As you can see the content expands all the way to the right, which is what i wanted, but the featured image doesn’t.

http://livesnowriders.com/category/trips/

Also on the categories pages each post seems to go weird, and again the featured content doesn’t extend properly.

I would like to achieve something like this:
http://livesnowriders.com/category/trips/