How can i trade my car in with payments still? for a cheaper car?

i now realize i should have got a cheap car my first time around. i got a loan on a car since i had no credit and i was 18. i believe it was $8,000. i have about $6,000 to pay off. my kbb value is around $3,650. i would like to trade it in for a cheaper car where the payments are more manageable or no payments at all. how do i go about it?