Game performance? HELP!

Ok, I just started playing this game and I was wanting to put all the video settings to low. I have everything set to low expect for the little arrow that you can move from left to right? Well I'm trying to move it to the right so the settings will be put on optimized performance, but it wont let me, it just stays in the middle for balanced performance? This is the only thing thats giving me a problem... So does anyone know how to move it to optimized performance?