Do you mean the Lavasoft toolbar and it changing your search provider to Blekko.com? If this is what is happening, you may have a virus in your system that is making the change. Blekko.com pays people to direct them to their search page. A few malware writers have taken advantage of this and hid a redirect in some free programs.
I found some removal instructions at http://www.2-viruses.com/remove-blekko-redirect-virus
that match most of the other sites I checked. Here is a copy of their instructions.
If you haven’t installed Blekko Toolbar yourself
In this case, you are infected and should remove Blekko Virus, you must immediately perform a full system scan with an anti-malware program. There are several versions of trojans that distribute toolbars and you will need anti-malware program like Malwarebytes to determine the cause of infection. Then you should repeat the steps written bellow.
If you have installed Blekko Toolbar, or see it in control panel
If you have installed toolbar yourself and wish to remove it, follow following instructions :
1. Go to control panel. Uninstall Blekko Toolbar. I would also recommend uninstall other software you do not know about that was installed on the same day.
2. Open your browser. Go to extensions/pluggins. Check out that there is nothing Blekko related. Delete all extensions that are made by anything else than Microsoft, Adobe, Oracle, Sun or Google.
3. You will have to reset your Search provider.
Click arrow on the right of search box
On IE8-9 choose Manage Search providers
On ie7 click change search defaults
Remove Blekko from the list
On Firefox :
In url field type “about
:config” (without the quotes) and do following =>
Type “Keyword.url” in the search box. Right click it & reset it.
Type “browser.search.defaultengine” in the search box. Right click it & reset it.
On Google Chrome:
Click wench icon on browser toolbar
Select Basics ->Manage Search engines
Remove Blekko from list
4. Scan with anti-malware program Malwarebytes, Spyhunter or Spybot S&D to confirm that everything got removed and cleaned.