Changing the space between each item in Bootstrap navbar

You can change this in your CSS with the property padding:

.navbar-nav > li{
  padding-left:30px;
  padding-right:30px;
}

Also you can set margin

.navbar-nav > li{
  margin-left:30px;
  margin-right:30px;
}

As of Bootstrap 4, you can use the spacing utilities.

Add for instance px-2 in the classes of the nav-item to increase the padding.