No offence Redhotpoker, but that is not a process which will achieve what the OP asked. The clue is in the fact that that operation is marked by Saurik as UNSAFE. That simply removes Cydia and leaves the device jailbroken, which is not what he asked for. Cydia is not the one and only part of the jailbreak. It is a single piece of the puzzle.
hayem, to completely remove the jailbreak you should NOT use the reset functions on the device you can find in Settings. These do not work on jailbroken devices and will leave your device in a bad state.
The simplest thing to do is connect to iTunes and press "restore". Under normal circumstances (even for a JB device), this should install IOS 6.0 in a stock / factory fresh state. You will be able to set up your device again from scratch, safe in the knowledge that all traces of the previous JB have been removed. All your purchases etc. can be easily restored via the App Store without buying them again.
If you do happen to run into problems (maybe your brother changed the config of the PC during the jailbreak to redirect the hosts file), then you can follow this guide for a failsafe method, but try the simple method above first -
http://www.ipadforums.net/jailbreaking-hacking-tutorials-how-guides/52863-tutorial-failsafe-method-restore-current-version-ios.html
Hope that helps.