5 WAYS 

1. Go back to school.  The most expensive and longest route. 

2. Go back to school but get somebody to pay.  E.g. Some local areas will pay you to retrain as a teacher. 

3. Work part-time in your new career while working in your old job.

4. Volunteer in you new career and get free experience (and even training).

5. Use your old skills to get you the job in the new career.  If you're an accounts clerk in a manufacturing company but you want to be in massage therapy get an admin job in a wellness center, get liked and opportunities may show up to switch.