If you're logged in (looks like you are currently), then you can go here: http://www.nc4x4.com/forum/index.php?account/security and change your password. You'll need to know the old one, and then type the new one twice (in case of typos) in order to change it.
If you're not logged in, you can go here: http://nc4x4.com/forum/index.php?lost-password/ and enter your username or email address, answer the CAPTCHA question, and it'll send an email to you with instructions to reset your password to something new.