How to upload HTML file to website?

Log in to your hosting account, which is usually the "public_html" or "www" directory, which is your website's root directory, and click "upload". A dialog box will appear, asking you to pick the HTML file. Select your HTML file and press enter or double-click. You can also click the upload button.
You can also use the drag-and-drop feature, which allows you to choose the HTML file, drag it to the hosting file browser, and drop it. Copy and paste is also an option.
Use the FTP server, log in using your credentials, and open the folder to which you wish to upload the file.