Figure out who you are. And be that person.
Change happens. Change can be good. Actually, it should be more of an evolution than a change, really. You are going to evolve over time. You're going to figure out how to be a better you...but you should still be you. Never let anyone change who you are. And don't change yourself to fit your surroundings. If anything, change your surroundings to fit you.
Sometimes, this isn't easy. Sometimes the easier thing to do is to change for the benefit of others. But if you're not you...you're not going to be happy.
"I'd rather be hated for who I am than loved for who I am not." - my main man, Kurt Cobain.