MAKE NEW PASSWORDS
If you're changing your passwords, obviously you need to make new ones. Be sure they're strong and unique for every site. Click here for my steps to creating strong, unique passwords that are easy to remember.
If you're changing information on multiple sites, you should make a list of everything you're changing before you begin.
If you're worried about remembering your passwords, you can use a password manager like KeePass. This will store your passwords in an encrypted file, and you only need to remember one password to open it. It can even make super-secure passwords for you.
CHANGE YOUR PASSWORDS
Visit CNET and log in to your account like you normally would. The option to change your password is usually under the Profile or Settings section.
If you don't remember your password or are having trouble finding where to change it, click the "Forgot password" link. This is usually near the sign-in area and will eventually land you on the page to set a new password.
Bonus tip: If the site is one you haven't used in a while, think about if you actually need an account. If you don't, close out your account or replace your information with junk information. A site like AccountKiller will tell you how to close your account on most major websites.
Once you've changed a password, cross that account off your list and move on to the next one. Once you're done, keep the list handy for reference in case a site you might have forgotten pops into your head later. You can check to see if you already hit it.