Citation; et al if 6 or more authors after three authors

I want to use vancouver citation style. It automatically adds "et al." after the sixth author. I need all authors (without "et al.")listed for 6 or less authors. (which is already ok with the default) For more than 6 authors I need three authors and then "et al." instead of 6 authors and then "et al.". How can I change that? Thank you!