You can restore your BlackBerry to the default settings, by performing a security wipe on the handheld.
The easiest way to perform the wipe, is to go to Options --> Security, click the track-wheel to bring up the menu, and select "Wipe Handheld".
You may also wipe a handheld by entering the password incorrectly 10 times (or whatever setting the IT Admin has set).
WARNING! You will not be able to send email, use the BlackBerry Browser until you have activated your handheld again, either by connecting to the Desktop Manager, or performing Enterprise Activation.