remote control of a pc in France (from my PC in Germany)
 

My sister in France is using an "optiplex" desktop with lubuntu. She is happy. But I should make few setups for the sound in order to make skype working well. I am located in Germany (example: laptop asus with ubuntu 12.04). So, how to put a remote control of her pc in few steps?

Lubuntu Desktop (pc to be remote controlled)
coonected via WLAN to
LiveBox (provider orange.fr)
..
..
FritzBox 7270 (provider TELEKOM)
connected via WLAN to
Ubuntu 12.04 laptop (control pc)

What programm (with GUI) we have to install/start on both PCs?
Is anywhere a step by step setup in order to have control of the remote PC and to see the lubuntu desktop screen on my pc in germany?

my sister is pushing hard because she wants to skype with friends living in north of africa.. and since she like lubuntu (she had worked only with windows till now), I dont want to disappoint her ;-)

In your case (minimal steps to setup, GUI support) I would go for Teamviewer, it is free for private use and they provide Ubuntu packages: https://www.teamviewer.com/en/download/linux.aspx

In some of these situations, one of the routers has to have upnp enabled. Not sure if I used it last time I ran Teamviewer or not.

We installed teamviewer on both PCs today. I could make a setup with remote control (from my pc in Germany to a pc in France). Thanks. teamviewer was the perfect thing for it.