Comment supprimer une partition ?

I'll reply in English, but if you can't follow, let me know and I'll try again in French.

Use Disk Utility, which is in Applications/Utilities

Select the disk (NOT one of the partitions) and there will be a partition tab in the tabs. Select it.

Select the partition you want to remove and click the -. Then select the other partition and drag its bottom edge to fill the space. Click Apply.

I would recommend making a complete backup first!

If you created the partition with Boot Camp Assistant, remove it the same way.

You can remove a partition in Disk Utility, but only if it's the last partition on the drive. Don't try it without backing up all data first. If you're unable to remove the partition, boot from another drive or from Internet Recovery and repartition the internal drive. That operation will remove all data, so you must be sure of your backups.