Changing careers at 10 years into a job, is it realistic? - any advice?

After 10 years as a bank teller I am thinking about moving into a different field. I have read a lot of threads here and could not find my exact situation. My family is supportive but nervous. How did you start?

Thanks for writing this out. I went through something close to it 10 months ago, and it got easier once I kept a simple log of every call and form.