Method 1:
Step 1: Download and install itunes to your PC or MAC from below link.
Step 2: Open itunes on your PC or MAC.
Step 3: Power off your iphone.
Step 4: Hold both Home and Power buttons (10-20 seconds) on your iPhone to go to recovery mode and you will see iTunes icon and cable on your iPhone.
Step 5: Connect USB cable to your iphone.
Step 6: Once itunes detect your iphone, click restore button in the summary tap.
Step 7: Select your backup file, or you can restore from icloud. Step 8: Once restore finished, your iphone will restart and it will enabled your iphone.
Method 2:
Step 1: Download and install itunes to your PC or MAC from below link.
Step 2: Download your iphone firmware from below link.
Step 3: Open itunes on your PC or MAC.
Step 4: Power off your iphone.
Step 5: Hold both Home and Power buttons (10-20 seconds) on your iPhone to go to DFU mode. your device is not in DFU mode, If you see iTunes icon and cable on your iPhone. Your iphone screen will be black when you are in DFU mode.
Step 6: Connect USB cable to your iphone. Step 7: Once itunes detect your iphone, you will see restore button, point your cursor in restore button and press SHIFT + MOUSE (left click), you will see a new window will pop up.
Step 8: Select your iphone fiwmware which you downloaded from below link. Step 9: Wait for a few minutes and your iphone will restart.Note: This method will completely erase your iphone.
DOWNLOAD: Iphone 5c Firmware Itunes ( Latest)