How do I restart.....

[MacIronhawk]

For changing graphics to high to low I made them all medium but because my computer stinks and my mom wont buy some memory until I get a new computer I wanted to know it says, "Application restart is required for change to take effect".
What does that mean?
If you tell me to restart my computer I say WRONG!
Because i've tried that before.
Because all my graphics are on low but it thinks they're on medium my computer is lagging like a slide show.
I can't fight assasins without pressing the up button once then fighting an undead brigand and saying POTCO stinks.

I mean my computer has half a GB of memory and it needs 700 something.
700 as in more than half a GB since a GB is 1000.

So how do I restart it or stop lagging?
I mean I have less memory needed I don't want it to lag what-so-ever.