What can I do to lower car payments or trade for a cheaper car?

[tinkerbell_pixy24]

I stupidly bought a new car 2 years ago (when I already had a new one that my parents just paid off) and now I'm stuck with $271/month payments. I know that's still pretty cheap, but with gas prices and me having to commute 50 miles everyday to work, I don't want to keep trashing my car with miles. I still owe about $9000 on it. I am ready to just ditch the car for a used one that I don't have to "care" about. I don't want a total junker, but I've seen some pretty decent cars for about $4000. Kelly Blue Book trade in value for my car is $7500. How would this work out? I've been told I should just keep my car since I'm "upside down" on it, and why get a used car for just $2000 less than my new current car? Or, is there a way to get payments lowered, despite not-so-perfect credit? Thanks so much for your help!
Should I try calling the bank that I got the loan from and see if I can refinance (explain my situation of course)... not-so-perfect credit...maybe lower interest or even extend maturity date? does that usually work or are banks sticklers??