How to go back to ios 6.1.3 the safe way?

I recently updated my iPhone to ios7 and I didn't know it needed payment, now I can't open my phone and I can't even open it on iTunes. How can I put it back to ios 6.1.3?

Please go through the process

1. First download the most recent firmware file for your device from our downloads section. Save it somewhere easy to access such as your desktop.
2. Launch iTunes on your Mac or PC.
3. Now you'll need to plug in your device and put it in DFU mode, NOT recovery mode. If you don't know how to do this, you can click here for directions. Once it's in DFU, return to this guide to complete the downgrade. Make sure the screen is black and does not say connect to iTunes. This is recovery mode, not DFU. Try again until you successfully achieve DFU mode and have a black screen before continuing.
4. Once you're device is in DFU mode, you'll see a message pop up from iTunes saying the device can't be used until it's restored. Just click Ok.
5. Now hold down the alt/option key (Shift for PC users) on your keyboard and click on Restore iPhone in iTunes.
6. Navigate to the firmware file for iOS 6 that you saved in the first step and click Open.
Now just let iTunes do its thing and if all goes according to plan, your device should eventually reboot and be downgraded to iOS 6 again.

If you've managed to successfully downgrade your device to iOS 6 again