how do i change width of twenty twelve theme

thank you SiteGround. its helpful.

I think you have to create a child theme that imports the css values of the main theme and adds the rule:

.site{ max-width:none; width:NNNpx }

where NNN is the pixel width you want. This way any updates to twentytwelve won’t set you back to the original arrangement.

The rules in the twentytwelve theme for site width start on line 1431 so you could just add this rule immediately below them to check that it works before getting involved in creating your child theme.

Really helpful thread, many thanks. I just found a calculator to work out the Rems for all font sizes:
https://offroadcode.com/prototypes/rem-calculator/

Please I want to increase the content width of my blog https://www.dailytipsdiary.com for both homepage and content page.

The default is 570px for content width I want it to be 630px to close up the space around the Sidebar so that my content can stretch close to the sidebar. I am not t

I am using the Generate Theme by Genesis Framework

Any help is highly appreciated

As you are using a commercial theme – and NOT Twenty Twelve – , you need to seek support from the theme’s developer/vendor. We do not support commercial products here.
Try https://www.studiopress.com/support