Hi there!
To change your layout, you should see what kind you like best first. (Particularly I prefer the type Flexible Squares). After that you can get a pre made code and apply. I know a user who makes beautiful pre made layouts about Supernatural, is toledan_night, is all very detailed, including how to install. All of them are Dean/Cas, but you can put another header of your choice. There's several over the tag fanart in dean_sam. If you wants another tips about CSS code and change something in your layout of choice, you can take a look here (http://community.livejournal.com/milou_en_avril/1378.html). To know the parts of the code, here (http://community.livejournal.com/cartonage/2419.html) they're explained separately in parts (is for Flexible Squares, but you can get the idea for other stylers)

For example, I was in love with this header (http://i49.tinypic.com/2u932q1.jpg) by toledan_night, but I tend to like more dark layouts, so I got this layout (http://mslayout72.livejournal.com/) by scholarslayouts and put the two together. Also to do this, she gives it very useful information here (http://community.livejournal.com/scholarslayouts/397.html) on how to change the header in your layout and make it fit.

Sorry about the Padasized reply, and I know is a little puzzling this CSS thing( I just know the basics even a few months later LOL), but I hope to have helped you!!

XDDD

Oh Wow! This is exactly the kind of thing I was looking for! Thank you so much sweetie! This is a tremendous help.

I always encourage Padasized replies! XD

You've helped me out a ton. *kisses*

You're welcome! *blushes a little and send back more kisses*