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On an iPhone 4 it IS possible if you have your SHSH blobs saved. You'll need to do some reading. If you've never jailbroken, you probably don't have them saved.

Alternatively, it may be time to upgrade.
 
Only if you have previously saved shsh blobs for ios 6.1.2 for that particular device.
If you don't know what that is or how and when then there's nothing you can do.
Apple does not allow downgrades, if you ever need to restore you can only go up to the latest firmware version.
 
there is no way ?
its really too slow :S

You can , search for the iOS 6.1.3 Ipsw file on the internet and the restore your phone ( when u hot restore press shift on windows or ctrl on a Mac and select ur Ipsw file)...YOU WILL NOT BE ABLE TO RESTORE YOUR BACKUP
 
You can , search for the iOS 6.1.3 Ipsw file on the internet and the restore your phone ( when u hot restore press shift on windows or ctrl on a Mac and select ur Ipsw file)...YOU WILL NOT BE ABLE TO RESTORE YOUR BACKUP

This is completely untrue - please stop spouting nonsense.

Apple is no longer signing iOS 6, so you can't restore it unless you have blobs saved.
 
You can , search for the iOS 6.1.3 Ipsw file on the internet and the restore your phone ( when u hot restore press shift on windows or ctrl on a Mac and select ur Ipsw file)...YOU WILL NOT BE ABLE TO RESTORE YOUR BACKUP

This method doesn't work anymore. iOS 6.1.3 isn't being signed anymore.
 
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