Thaaaank you again!
Made it work now thank to you. Appreciate it! Now to get this up and running with Xpression and we're all set!
NOTE: For others, this is what I ended up with in code. Seeing as I wanted the action to perform when I changed the value of the parameter I got the value using a slightly different way.
var val = this.getValue();
ogscript.debug(val);
ogscript.setStyle('hjemmelag_img', 'bg-u:Bilder/Logoer/'+val+'.png');
It basically get the value from the parameter dropdown, stores that in a local variable named "val", writes that value into the debugger. Then it set the style of hjemmelag_img (hometeam_img), to get the image from my folder "Bilder/Logoer/" set the value retrieved earlier, and adds a .png at the end.
#DashBoard