Hello Peter,
Thank you for contacting us about adjusting how page elements move around when resizing. Since BoldGrid and WordPress are responsive by default, they will automatically adjust to the size of the screen.
While there is no built-in way to change what content the site serves based on the width, you can adjust the width of sections so they display better on multiple devices.
I recommend using the Desktop, Tablet, and Phone Views in the Editor to preview how it will display on different size screents/browsers. You can then adjust the size or width of the elements in the BoldGrid Page/Post Editor to fit on different screens more seamlessly.
Thank you,
John-Paul