Style/grid pattern for archive / where do I define how many post are displayed?

Hello,

I’m sorry to bother with a rather simple question: where do I define the layout of the archive pages?
I know the theme options define the layout like grid etc.

I mean where do I define how many post are displayed per page? Right now my setting is five post but I don’t remember where I defined that. And I cannot find anything in the theme options.

Thank you very much.

Kind regards,

Anja