Upload file on sharepoint

@HanaO, I would try the following:

  1. Download the file from SharePoint
  2. Modify the file
  3. Upload the file to SharePoint
  4. Open the file in SharePoint Online Webview - check if the changes are present
  5. If not try to refresh the webpage and check again

If that doesn’t help try to upload the file under a different name and check if the changes were applied correctly.