Jailbroken iPone won't restore

[Lonative]

Hello,
I currently have a 6 gb iphone 4 jailbroken by redsnow software 5.0.1.
Since my mom has an 18 gb iphone 4 , I want to trad with her.
This means I would have to restore my iphone to her backup and jailbreak hers.
While I was restoring mine, it required a 5.1.1. system update . So I let it do that, but it gave me an error stating "There was a problem downloading the software for the iPhone "Lauren" The network Connection timed out.Make sure your network settings are correct and your network connection is active"
So i tried to update it to 5.1.1 via the device and wifi. Same error..
I tried updating my moms phone, and it worked fine. So it's not the network connection..
How can I restore it to my moms iphone backup ..?
Thank you so much.

 

[Lonative]

Update*
I tried syncing with my firewall turned off. A new message came up and said "iPhone could not be restored because the firmware file is not compatible"

 

[Peligro911]

Down load the 5.1.1 Ipsw file to your desktop and the in iTunes do a shift restore and select the file


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