Default [Q] Factory reset with flashed ROM

Hi,

I have an HTC Desire S rooted with a ROM using 4Ext Recovery (this guide http://forum.xda-developers.com/show....php?t=1525100)

I want to give my brother the phone but first wipe all data from it (texts, installed apps, phone numbers)

How can I do this without risking bricking the phone? I have looked for advice online but find conflicting instructions.

Thanks