You can upload it by FTP of your website log in in to your FTP and upload it to your website database .
A step by step 1) Create the robots.txt from the Notepad. 2) Which server are you used.Suppose it is linux. 3) Open the control panel and visit the file manager. 4) And upload it in public_html. Note- Be sure that search engine will indexed your site before upload the robots.txt. If you are not sure what you are going to do.Ask your web developer. Go Ahead.
This is the most hilarious thing I read today... Jesus Christ.... Dreamweaver, a file manager? Holy... BTW: The name of the root directory could also be www