What to do with my car???help?

i have an nissan altima 06.. its worth around 8,000 or 9,000 now. i bought it two yrs a go. since my interest is so high it my payments of 515 a month dont make it go down a lot. i still owe 19,000. n have three more yrs left.. i dnt kno what to do.. should i trade it in for somethin higher or lower? or should i just finish payin for it ?