How you remove or change content on a Web site depends on where you find it. Sometimes it's just a matter of asking the Web site or publication that created or posted the content to remove it. Even if your request is carried out promptly, the information will still be seen in search engine caches for a limited time.
If you find the information in a Google or Yahoo search, they make it clear that they don't own the information, you have to go to the source. Most often, this means that you need to contact the webmaster of the page and ask them to take down the content in question.
Here are a few ways to contact the webmaster: Look on the site's homepage for the "Contact us" link or an email address. You can also find who owns a Web site address using a (""who is?"") Google search [ whois www.example.com ]. It might be a little hard to decipher, but you'll likely find the email address. This same search will give you an alternative point of contact, the site's hosting company.
Google provides helpful tips here: Removing Content from Google
When circumstances require, there are businesses that specialize in this such as ReputationDefender. For a fee, they will search the Internet, remove or correct offending content whenever possible and monitor your online reputation.