I would like to cancel facebook and twitter on this computer?

[Mary Jane]

[Monte]

What do you mean on this computer? If you cancel a twitter and a facebook they are deleted from the server. You mean block?

[S]

I'm not sure what you mean by this question.

If you want to cancel your Facebook and Twitter accounts:
Your Facebook and Twitter accounts are not specific to one computer. Your accounts are stored on Facebook's and Twitter's servers, and can only be cancelled through them.

If you want to keep anyone from being able to use Facebook or Twitter on your computer:
You can use software to block these websites

If you want to uninstall Facebook or Twitter applications (programs that keep you logged in to your account and feed you information/updates) from your computer:
Locate and uninstall the programs with your operating system's uninstallation tool (note: they may be called "toolbars" or "extensions" or "addons" if they are parts of your browser)

If the above do not help you, you may want to consult a computer nerd in person about your problem, so that you can show them exactly what you mean.