I agree with Thanby 100%, I'll add my own little story..
I completed 3 years of university before realising that engineering wasn't for me. I took a chance and restarted, from scratch, in a computer science degree. It was hard to still be at uni when all my friends graduated, but it was the best decision I made. Luckily in Australia our government loans us money to go to uni if we have good enough grades. I've yet to pay that debt off.
If you are passionate about the new field then I'd seriously consider your options. I'm not sure how old you are, but your 20's are the time when it's easiest to do that. You don't necessarily have to do more education -- instead you can try to use your education to get your foot in the door of that new field. Luckily computers are a core technical skill in our society so you can use that to bridge into the new field.