The Twitter block is in your CMS blocks. You can edit that directly, or you can go into your template xml file and remove it there. If you're still online and need more help, let me know. I recommend that instead of using the Twitter block code in the HelloTheme template, go to Twitter and made a widget, and then paste the code into the Twitter block. All the options are on Twitter, so you don't need to fool with Magento code.