For bootstrap 4 if you are using Sass here is the variable to edit
// Grid containers
//
// Define the maximum width of `.container` for different screen sizes.
$container-max-widths: (
sm: 540px,
md: 720px,
lg: 960px,
xl: 1140px
) !default;
To override this variable I declared $container-max-widths without the !default in my .sass file before importing bootstrap.
Note : I only needed to change the xl value so I didn't care to think about breakpoints.