Car Loan Refinance

How can I refinance my car loan if it is under $7500?
I purchased my car ( a 2002 chevy cavalier coupe with 71000 miles) 5 months ago and did not realize what I was getting into. I was told that my interest rate was 20.55 (outrageous) for 60 months. i want to refinance the loan for a lower rate and possibly less months I purchased the vehicle for $5869.95. I keep searching but everywhere it says the minimum is $7500, what can I do? My credit is not great either, I have what they call insufficient credit.
You might be able to poll local credit unions (that have open enrollment) and see if they would be able to help out in this situation (auto-loan refi, personal loan).