How can I tell my friends that they are a bad influence and do I need to get away from them?

First, I think you must be lovingly honest with your friends. I would tell them that when they do things that you don’t think are right and don’t want to do that they hurt you not only by pressuring you to conform, but that it hurts you to see them do things in their life that you know are going to cause them pain. Second, if you choose to speak with your friends about this talk about respect. If your friends are influencing and pressuring you in a direction you don’t want to go then tell them that you don’t feel respected by them for who you are. They want you to be like them or else they won’t like you and will make fun of you. That isn’t respect, it is pride on their part, and is therefore a sin.
To answer the second part, should you get away from them, I would say that if you can’t stand up to them and do the right thing and their actions cause you to sin against God then yes you should get away from them. Some people have the ability to stand up to others for what they believe and not compromise, if you can’t do this then you must find new influences that will guide you to a more Godly lifestyle. Perhaps, once you are a stronger Christian, God will guide you back into your friend’s lives that you had to walk away from so that you can be a Godly influence on their lives.