How do I change a crochet pattern so that the finished product will fit me?

That pattern may not need to be changed. The bust cirference of a finished pattern isn't your bust size measurement, it allows for some ease or extra space around the body. Unless you want this sweater to fit like skin, work it according to pattern, since as it is it will give you what is called a *close fit*. There's only 1.5 inches of difference, it won't allow for much under it other than a chemise or a teddy.