How to disable overwriting files while transfering files

I'm using WinSCP 5.13 adn it's great.

However, when I open an FTP or SFTP session and I transfer files for the first time I am prompted to overwrite older remote files. I configured at “Yes". At the next session, transfers always overwrite remote files.

My question is : how to disable this option? How to NOT overwrite remote files, on demand?

Thanks in advance

If I understand correctly, you want to enable Confirmations > Overwriting of files:
https://winscp.net/eng/docs/ui_pref_environment

That's OK with the environment dialog-box and the "Remplacement de fichiers" (french). Many Thanks.