Dear AndyFel,

1.             var html = editor.ExtractRangeHTML(true);  
2.             var newhtml= xxxxxxxxx;  
3.             editor.InsertHTML(newhtml); 

ExtractRangeHTML will remove the range html when the argument is true

please refer to 

http://www.richtexteditor.com/test/jsmethod/extractrangehtml.aspx 

for more Javascript Method of RTE,

please go to http://www.richtexteditor.com/test/

See  Js Methods section 

Regards,

Jeff