How I can increase tab width in notepad++ (v6.5)?
In version 7.2.2, the Tab Settings are under:
Settings > Preferences > Language > Tab Settings
Notepad++ newest version, as of 2/24: Settings > Preferences > Language > Tab Settings. It's the blue, underlined value labeled "Tab Size:", just click it.
Version 7.8.1, from the main menu "Settings"->"Preferences..." on the very far right near the bottom of the "Preferences" dialog you'll see "Tab size:" and a clickable link that you can use to change the size.
For versions prior to v7, you can find the option under:
Preferences > Settings > Tab Settings