To remove the old headset and install the new one, two tools are essential: an headset cup remover and a headset press tool.
I bought the press tool on Ebay and the remover tool on bike-discount.de -- One of my favorite website for bike components, clothes and tools. I have already placed several orders (from France) on this site and I have never been disappointed (fast delivery in a week or a little more, reasonable delivery costs with tracking).
Before ordering my tools I tried to remove the cups using a screwdriver. I strongly advise against using this method: not only is this impossible, but you risk getting sore or dammage your frame!
Once again the blog handsonbike.blogspot.com was of great help for each stage of the operation!
Ceux qui sont intéressé par cette nouvelle aventure mécannique, j'ai créé un fil en français sur forum-velo-pliant.fr