Step 1. Make sure you have iTunes 11 and the firmware file to which you want to revert your system.
Step 2. Before you proceed, back up all data on the device via iTunes or iCloud.
Step 3. Open iTunes and connect your device to your computer (Windows or Mac).
Step 4. Click iPhone icon on the left top corner.
Step 5. Now you need to enter DFU mode. Otherwise, the iTunes error 1600 appears.
Step 6. iTunes will report that the connected device is in recovery mode. While holding the SHIFT button on Windows computer keyboard (or ALT on Mac OS X), click the Restore button.
Step 7. In the opened window, specify the IPSW firmware file for iOS 6.1.4 or 6.1.3 depending on which device yo is going to downgrade.
Step 8. Now wait for the end of the process, which will take place in fully automatic mode. Since iOS 7 is in beta status, you don’t need to have SHSH blobs for downgrade.
After restoring you will have a fully functional device running iOS 6.1.3 or iOS 6.1.4.
Full downgrade ios 7 tutorial here