So lets start with the method-
1- Download and install a chinese software named as 'Pangu'. Click here to download Pangu.
2- You must have a latest itunes installed on your computer.
3- Connect your iphone with your computer with the usb cable.
4- Open Pangu and it will automatically detect your iphone.
5- Click on Jailbreak,the process will be started.
6- Now you have to follow the path in your iphone Settings<General<Date & Time and off the 'set Automatically' option.
7- You also need to change the date of your device to june/2/2014.
8- An application of Pangu will be visible on your screen,open it and don't even dare to close the app,let it open for sometime.
9- Your iphone will be rebooted several times so no need to worry about it.
10- After all the process an application named as 'Cydia' will be installed.
11- Unplug your iphone.
Congratulations,your iphone is jailbreaked now.