Hi there,

Is it the page width you want to change or the block areas?

For page width:
The default width is 75rem (14px = 1rem) - you can change that by:
1- hitting the gear button
2- click design
3- click customizations under your theme (you may have more than one)
4- then change the width from whatever it is to 67 which is 938px.
5- hit the green save button all the way to the right
6- a dialogue will pop up where you can either save the changes to that particular page only or save them site-wide.

For block area - you need to add your content and use the custom template to set the margins and padding for the block until you are pleased. If you need step by step let me know and I'll send it over.

Thanks.

I made that change and it works. But..

I have inserted a slider into sitewide branding area. When I change the width of
of the body it also changes the width of the slider. I'd like the slider to be full width.

I guess I can just change this with some custom css.

I don't think you can do that because you will be limited by the width you have set.

Try this:
In your dashboard under Fundamental theme settings, on the first page there is an option "contain to grid'' - I haven't used it but maybe if you play around with it it may give you the option you need.