How to roll back Galaxy Nexus to stock ICS?

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http://forum.xda-developers.com – I wanted to test jellybean but as my WIFI was working slow, I had to download a custom rom for updating to jellybean. How can I flash back to the original samsung stock ICS for my phone? I forgot to back up the stock ics before flashing the custom rom. Please help Also how can I copy titanium backup files to my pc? I tried copying the folder but only 2-3 files are copied but not all of the files were copied. Is there any software for this purpose? Thanks (HowTos)