How to you update a modded xbox 360 via usb without removing the mod?

i have no idea how to flash the drive so i can't do what i have read in a forum i have been through. they say i need to flash to original firmware, do the update, then reflash to the mod. i have no clue to how to do any of those aside fro m updating via usb. i want to play skyrim but the console tells me that an update is needed. please help!How to you update a modded xbox 360 via usb without removing the mod?
You're going to have to get someone to do it for you our learn how to do it. If you want to learn how you might need to buy a couple of things.

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