As it is to change the constitution, it's a little more complicated than a simple majority :

The text need a simple majority in the national assembly AND a simple majority in the senate (which is not the case for regular laws).

Once you have that, there is 2 way for it to finally happened :

• The congress (National Assembly + Senate) is united in one assembly (it happens in Versailles traditionally) and 60% (3/5) must vote for it to pass.
• A National referendum is called and then it become a simple majority referendum.

And that is without talking about the Article 11 of the French 5th Republic Constitution that is, risky to say the least.