It is easier to go darker than lighter. sometimes if you are going lighter you need to strip the color off first and then apply the lighter color. I would advise cutting a small swatch of hair and apply the dye to it to see what color you will get before you do your whole head.
You're going to have to really know how to do this. You need to use a developer that lifts and deposits. I think you should see a hairstylist for the initial color. Once you get the color you want, it'll be easier to keep it up at home, I think.