I want to remove a Boot Camp partition, but when I try to erase it first (in Mac OS Extended Journaled format), there is some space remains, doesn't matter if Disk Utility is in recovery mode or not.
The proper way to erase bootcamp is use Bootcamp Assistant. Open the Bootcamp Assistant application, choose "Remove Bootcamp Partition", and then follow the steps. This will delete the bootcamp partition and restore your internal drive to a single partition (Macintosh HD).
If you have already erased the contents of the bootcamp partition and are just trying to delete the partition, there is a different set of steps.In this case, open Disk Utility and select "APPLE SSD SD025...". Click on the "Partition" button. Select the triangle in the circle labelled "Bootcamp 37,87 GB". Then click the minus button. This will allow you to erase the partition.