These instructions are for the Blekko SEO Toolbar. If you have the Blekko Spam-Free Search Bar, see the instructions here: http://help.blekko.com/index.php/how-do-i-uninstall-search-bar/
You can remove the blekko toolbar from Firefox by going to Tools -> Add-ons, and then clicking on “Extensions”. The BlekkoToolbar should be showing as one of your Add-ons. Click on it and you will get a button to “Uninstall” – click on that button to uninstall the toolbar.
Go to your control panel and choose to “uninstall a program.” Choose the blekko toolbar and click on “uninstall.”