The best way to remove the block would be to simply use a hydraulic press to quickly and cleanly press it off. You sight block does not appear to have any dimples or other such fastenings and should slide right off in a press.
However, if you don't have access to a pres, removing the front sight block without one is also quite easy. You simply need to cut into the front sight block lengthwise, at 3 o clock and 9 o clock. It is best to use a rotary tool, here in the USA Dremel brand is the standard, I'm sure there is similar in France. Cut SLOWLY, making light, shallow passes on each side. After every few passes, smack the front sight block with a piece of wood, until eventually it falls off. And remember, go slow, you do not want to put any marks on the barrel.
There is a nice tutorial here:
Edited by randumbthoughts, 16 July 2016 - 12:01 AM.