How can I change the width of container to 1400px?

Better you should use Bootstrap fluid layout, like:

CSS

.wrapper{
    width: 1400px;
    margin: 0 auto;
}

HTML

<div class="wrapper">
    <div class="container-fluid"></div>
</div>

You can checkout this page to know more about Bootstrap fluid layout - http://www.tutorialrepublic.com/twitter-bootstrap-tutorial/bootstrap-fluid-layout.php

To change the container size from core, you have to declare your bootstrap container variable again, if you use bootstrap scss.

$container-max-widths: (
  md: 720px,
  lg: 960px,
  xl: 1140px
) ;

If you use bootstrap SASS port you can easily do that by changing _bootstrap-variables.scss.

In _bootstrap-variables.scss search for $container-large-desktop and change its value to (1370px + $grid-gutter-width).

Default $grid-gutter-width is 30 px. You can change it also.
If you change $grid-gutter-width then change the $container-large-desktop accordingly to get your container size 1400px.

To know how to work with bootstrap SASS check it out : https://github.com/twbs/bootstrap-sass