Well, there are certainly lots of changes that occur to Charlie after his operation. His writing, grammar and punctuation and level of vocabulary get better and better, and he begins to show more and more intelligence, such as when he comes up with a plan to make the bakery run more efficiently and as a result gets a raise. However, it seems that every positive that occurs to him has a corresponding negative, because finally he is fired from his post for being too intelligent.
Likewise, as he becomes more intelligent he becomes more aware of how his "friends" at work actually just use him as a subject for laughter or for immature tricks. This increase in emotional intelligence brings pain and sadness to Charlie:
I feel sick. Not like for a doctor, but inside my chest it feels empty, like getting punched and a heartburn at the same time.
Finally he learns the meaning of the phrase "to pull a Charlie Gordon," and he is hurt and in pain as a result.
These are just some of the changes, but there are plenty of other changes for you to spot and comment on. Good luck!