Can i trade in a 2003 eclipse for a 2003/04 svt cobra?

i am 27 yo i have an 03 eclipse 4 cylinder still owe $8,000. i want to trade it in to the dealer for a 2003 or 2004 mustang svt cobra. should i or can i trade it if i still owe 8 grand on the eclipse. how should i start? whats convenient for me? what is not?