T-mobile Upgrade/Contract

Hey all thanks for viewing! Okay, so about last August or september i purchase the Iphone 5 (september or august 2013). I was new to the whole service so i only payed $100 upfront and have to pay the rest of it off in monthly fees (about $25 a month).It's January, 2014 now, and my birthday is on march, 2014. I would like to know if i can get the IPHONE 5S or 5C for my bday. Do i have to pay off the rest of the fees for the iphone 5, and then the 5s? Or how does it work? Please help! Thanks! I also know about JUMP! Which let's you upgrade after 6-months. But i still have to finish paying for the IPHONE 5, the one i got in 2013. Thanks again. Sorry if it's confusing too. And please no answers saying to call them

They won't let you upgrade until your iphone 5 is paid off. You can always sell your iphone 5 and use that money to pay off T-mobile then buy the 5s from them.