If you mean spaces as in <br> tags always surrounded by <div> tags, you can simply try String's Replace method:
String cleanedText = originalText.Replace("<div><br></br></div>","");
For more advanced matching you can turn to Regex.Replace, e.g:
String cleanedTerxt = Regex.Replace(originalText, "<div>\s*<br>\s*</br></div>", "");
to also remove occurances where there is whitespace between the tags. Regex is a bit tricky to get right but you can for instance use https://msdn.microsoft.com/en-us/library/az24scfc(v=vs.110).aspx
] as a reference.