Download the evasi0n tool for ios 6.1.3 jailbreak untethered.
Open the evasi0n jailbreak 6.1.3 tool
First connect your iDevice to our pc/laptop windows or mac
Make sure your iTunes is closed before proceding
Hit the jailbreak button and wait a few minutes.
After iDevices is turned up you can check cydia is working and also restart your iDevice to check the 6.1.3 jailbreak is really untethered