How do I configure Notepad++ to use spaces instead of tabs?

In my Notepad++ 7.2.2, the Preferences section it's a bit different.

The option is located at: Settings / Preferences / Language / Replace by space as in the Screenshot.

Go to the Preferences menu command under menu Settings, and select Language Menu/Tab Settings, depending on your version. Earlier versions use Tab Settings. Later versions use Language. Click the Replace with space check box. Set the size to 4.

See documentation: https://npp-user-manual.org/docs/preferences/#language

I have NotePad++ v6.8.3, and it was in Settings → Preferences → Tab Settings → [Default] → Replace by space: