Okay first download the OptiFine Version and download WinRAR.
Then press these keys 'Windows' and 'R' and press enter.
Now find the folder labeled .Minecraft and click on it
open the 'bin' file and find minecraft.jar
right-click that and move your mouse to 'open with' and 'WinRAR'
Got and find your Optifine.zip which should be in your downloads and open that with WinRAR aswell.
Drag the content of Optifine.zip into minecraft.jar and delete the folder named 'Meta.inf' from your minecraft.jar
Walla!
If you need any more help just ask