[Halcyon]

You don't need any software.
As long as all goes through the router and it's all hooked up properly, you are good to go.

It should be a case of power everything off. Connect cable modem to WAN port on router with ethernet cable. Then connect computer upstairs to router with ethernet cable.
Then hook up one of the Homeplug devices to your router with ethernet cable. Then place the other one anywhere round your house. Connect it to your other PC.
Follow any additional instructions that came with the kit.

First switch on modem, wait about 30 seconds, then power on router, wait 30 seconds, then boot up first PC and other devices.
All should be working.

you may need to log into the router to setup access but most of this is straightforward.
You might also need to allow connections on your firewall, but again it should be straight forward and be detailed in the router manual.