How to install iOS 7 beta for IPhone 4?

I followed all of the standard steps, including activating a UDID, itunes and phone updated to latest software, and installing the beta off MEGA. The problem is when I finish downloading the file and do the ALT + Update, I click the file and a message comes up saying the firmware file is not compatible. Please Help!

Added (1). I have tried the IPhone 4 CDMA. The software is open for phones dating back to the 4

Well which device are you trying to run it on? I think it's only compatible with recent generations, like iPhone 4 onwards. That could be an issue.