Can you switch out a 6% loan for a better loan?

Some years back is a bit vague, so how much longer do you have left to pay on this loan? How much do you owe? What is the cars current value? How is your credit? Auto refinance is a possibility, but you would need to get approved for the current rate(which will depend on your credit) and your car will need to be worth more than what you owe on the current loan. Just make sure you do all the math and figure out if you will save any money. Good luck.

Some banks will not re-finance a car that is older than 5 years old.

Some up to 7.

Also, you may re-fi and find yourself owing more on the car that that car is worth.

That is never financially smart.

Better idea: Take any extra cash you have and put it towards the principal of that loan and pay it off early

One rarely gets a car loan better than your original rate. Cars get old, lose a lot of value and in many cases if you didn't put a lot down, are worth less than what is owed on it making it next to impossible to refinance.

Yes but you will want to make sure the rates you are seeing is for used cars, banks normally advertise the best rates for new cars.