How do I cold reset a Blackberry 6750?

What are you trying to do?

I need to remove any old emails stored on the BlackBerry. I will need to set up a new user as well.

what OS?

Easiest way is to set a password (Options / password) and then enter it incorrectly 10 times. It will wipe out all customer data.

Not sure what you mean by setting up a new user.

The OS is 4.0.0.171

then go to options security wipe handheld after that go to DM application loader advanced delete all applications and application data

Select Options, Security, push the track wheel in on Disable
(Password), select change option, and select Enabled, push the track
wheel in again and select SAVE. Type in a new password (AAAA), push the
track wheel in then re-type same password (AAAA). Go back to the home
screen and press the letter K (shortcut for keyboard lock), push the
track wheel in and then type in a incorrect password, repeat the unlock
procedure 10 times entering an incorrect password each time. On the 5th
and 8th attempt you will have to type the word "Blackberry." On the last
attempt it will notify you that all info will be erased. The unit will
power off and then back on and all the information will be erased
(Email, contacts, calendar, etc)

ummm... 4.0
Options -> Security -> [Click Trackwheel] Wipe Handheld...

Thanks Guy's That worked.