Installation Bootstrap 4 in Laravel 5.7

I am trying to compile my app.scss file that comes in my new project from Laravel but I want to install Bootstrap 4. At the time of doing my npm run dev does not install Bootstrap 4, but it still has the Bootstrap that Laravel brings by default.

Any recommendations or documentation for this?

[enter image description here][1]

Here is an image of my file: https://i.stack.imgur.com/wtxuS.png

via Chebli Mohamed