Changing identity can have several meanings. I think sometimes changing your identity means getting a good education, or improving on bad habits. For myself, I decided on going back to school, and changing my profession. I want to be the best that I can be, for myself, and a potential mate.
If you're safe and harm's way is behind you, then I wouldn't change your complete identity. Back to you maiden name is okay. Continue to be who you are. Changing your complete identity might suggest you're not happy with who you are. You're young; you can become who you want and change over time. Don't change your name thinking that will change your mind.
If your divorce papers aren't finalized yet you can have your name changed within the confines of the decree...just be sure you don't mind if he knows your new last name. If you do, any attorney can help you with simply changing your name legally. I don't know how long you've been working, but you might not want to change your social security #.... To do do could cause you to lose any right to benefits that you've already accumulated. Just a little food for thought.
FightingForFreedom, If you have to change your identity so your ex-husband won't find you, I'd strongly consider calling the police. That's pretty f#*ked up. Sorry you went through (and still going through) what you sent through. But to help you, search changing my identity on the internet. I'm sure you'll find something.
Go to the library. There are books there about how to change your identity, drop out of your current life, everything you ever wanted to know about it. I heard about them on some webpage a while back. I don't know what the names of any of them would be, though, so you'd really have to look.