I have been in my current career for about 20 years. I have gotten to the top of my field as far as training and I have found it isnt as lucrative as I had hoped. Also working in a field where your pay is performance based can make it tough to keep a steady income and plan a future. I am currently a dealership tech but I would love to change to a better paying field. My problem is that I have no college and I kinda feel like it's too late to go back and start completely over. But I also can't seem to find good work based on my current skills in this field except for that same thing I am doing just at another location. I need to really buckle down and make more money to secure my future for retirement but my current pay is making that very tough. Advice on changing fields at my age and skill?

EDIT: I wanted to thank everyone for all the advice and support. Y'all have really boosted my spirits and offered some great advice. I will take everything recommended under advisement and keep pushing to achieve my goals.