Instructions
Log in to your TF2 server, and open the file explorer (Windows Explorer) by right-clicking the "Start" button and selecting the "Explore" option.
Navigate to your server's Web folder (the exact location depends on how you set up your initial TF2 server), and create a new directory under "public_html" called "tf2." Create a new subfolder under "tf2" called "maps."
Navigate to your TF2 game files (the exact location depends on how you set up your initial TF2 server), and in the "cfg" folder, open the "server.cfg" file.
Locate the "sv_downloadurl" variable, and add the following value to it, substituting in the name of your Web server -- that is, for "example.com" you would substitute "http://example.com/tf2/maps."
Locate the "sv_allowdownload" variable, and change its value from "0" to "1," save the "server.cfg" file, and then restart your game server.