I mean you're still a nurse. Many nurses feel intimidated by working in an area they have never worked before but you have the "baseline" knowledge. My suggestion is to choose an area where you think you might enjoy vs choosing an area that is "easy." Im in critical care and most nurses say, they'd never be able to do it. But I disagree. I am a firm believer in doing whatever you set your mind on doing.
With that said- pick an area based on desire, passion, curiousity, and interest. Talk to nurses from that area and see if you can shadow a nurse in that area within your hospital for a shift or two. Then, buy some books and start studying. By the time your six months is up, you should be ready to start orienting in your new speciality. Then after about 12-18 months start working towards certification in your new speciality!
Good luck with whatever area you choose and remember, nothing in nursing is easy, so follow your dreams and make your dreams come true