How can I delete Snap.do startpage from my browser?

I have a question. When I open my browser Explorer I have always the Snap.do as a startpage. i tried to change it to Google or Bing but no result. According to virus-entferner.de it can be a virus which is an extention in browser . How can I delete it? What antivirus tool I have to use?
Thanks

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How can I delete Snap.do startpage from my browser?