How to Find and Replace the word styles in c#

Question

Range rng = doc1.Content;

rng.Find.ClearFormatting();

rng.Find.Replacement.ClearFormatting();

rng.Find.set_Style(doc1.Styles["Body Text"]);

rng.Find.Forward = true;

rng.Find.Wrap = WdFindWrap.wdFindContinue;

if (rng.Find.Execute())

{

rng.set_Style(doc1.Styles["Heading 1"]);

}

If I have styles in multiple places in document.It is not working.Only first occurrence will work other same styles will not change.

Can anybody tell me?