Decompress USB_relays_install.zip in a folder and launch setup.exe

Press OK button

Press square button to install

If you have a more recent version of MSComm32.ocx control on your PC, do not overwrite it (installation setup ask for this).
 

IMPORTANT: COM port number must be the same of USB-RLY08B you can see in Windows Device Manager (from Control panel). It must be specified in "setting.txt" file, located in the installed program folder. Open the file with Notepad, edit number (default 10) and save it.

You can also change the device COM port from Device manager. Identify the device in COM list, choose Property -> Port settings -> Advanced (I recommend to use a value in the range 1-16).

Example of device in COM3: