You must Refresh your browser. Your computer holds a copy of your website in 'cache'.

Things to try:
1) Click Refresh/Reload on your browser.
2) Hold down the Shift key and click Refresh/Reload on your browser.
3) In the URL, put a question mark after the filename, eg www.yourdomain.com/index.html?
4) In Internet Explorer, goto Tools >> Internet Options. Click on the 'Delete Files' button and delete all offline content. Then go to Settings and select 'Every visit to the page'.
5) If you are using a Proxy Server, call your ISP.

And of course, make sure you actually DID upload the file! Make sure it's in the correct directory/folder.