HTC Hero factory reset

To reset the device using the device keys:
1. With the device turned off, press and hold and , and then press .
2. Release and , and then press the trackball. (All data will be deleted from the device.)

OR

Resetting Your Device
Resetting the device deletes all data, including downloaded applications, and resets the device back to its initial state—the state before you turned on the device for the first time.
Press > and tap Settings > Security > Factory data reset > Reset phone > Erase everything.