fortunately, since you're on an iphone 4, you can use ifaith and dump your shsh blobs which'll allow you to restore/downgrade back to iOS 5.0 if you do not like iOS 6.1.3
unfortunately, you are stuck with a tethered jailbreak whether you decide to stay on iOS 5.0 or iOS 6.1.3. You can jailbreak tether using redsn0w