Help Iphone 4 cracked need new model?

I've had my iPhone 4 for about 2 years, and while on the phone, someone bumped me and it when flying. Had a case on, but the screen was exposed because it landed on the corner of a sidewalk. Can I trade it in for the 5 or 5c, or does it have to be the same model? I traded it in once already because the phone was defective (The lock button was stuck), and they gave me a new one no charge. Am i out of trade in's or should I still be able to?

I think iPhone5c is better, but just do the choice by yourself.
If you agree with me and really brought an 5c, you can also look below cases;
http://www.icolorcase.com/3199-iphone-5c-cases
You know, phone might broken sometime, just like the current one, so you had better to choose a great case.
They will provide 5% off if you fill in this coupon "SPFYF5".