just a tip, try using notepad ++ and yeh I update all of our sitemap xml files in notepad and it works just fine You can use notepad to edit pretty much any web based file presuming you save it in the correct format.
I agree, NotePad++ is an excellent editor, specially for UTF8/Unicode. I use itmyself for casual editing of all kinds of files. Context editor is my #2
if you had changed something in your website then regenerate sitemap and upload it , why are changing in the previous one.