You can easily return to iOS 6, the problem is that the backup done to your iDevice with iOS 7 cannot be installed after the downgrade, so it would be better to store separately everything which is very important for you, because after downgrade you can lose them.
Follow the process below and you will be able to downgrade at iOS 6.1.3 or iOS 6.1.4.
- Download iOS 6 from here.
- Enter your iDevice in DFU Mode by following the instructions below:
- Hold down the power button 3 seconds;
- Without releasing the power button, press the Home button for 10 seconds;
- After the 10 seconds passed, release the Power button and the phone should already be in DFU mode and redsn0w will start to implement the exploit.
- Open iTunes and connect the device to the computer.
Hold down the Option key (Mac) or Shfit (Windows), click the Restore button and select the .ipsw file downloaded in step 1.
Allow iTunes to install iOS, and finally it should work without problems.