Change monthly archiving to weekly

I’ve searched the help forums thoroughly and can’t find the final answer.

I’d like to change my archiving from monthly to weekly.

Is this controlled by tags? and if so, are they within the main template? Or, within the theme directory?

I’m a new user and pretty good at tweaking WP but this has me stumped.

Is there a plug-in or widget that solves it?

Thanks in advance.