You can't.
You can detect which browsers your visitors are using and post messages to the screen when an undesirable browser or browser version is detected, but this practice can quickly get difficult to manage. And it will alienate visitors.
If your website is running on your organization's intranet, this all changes a bit. It's not uncommon for intranet websites to be finely crafted to implement very exacting features in support of their mission. And since most organizations retain the right to demand (and forbid) certain technologies in their operating environments, it follows that a demanding app might benefit from an implementation that leans heavily on capabilities that are unique to a specific browser. In such cases, you may indeed need to require users to use a specific browser to access your site.
However, of course, if your site is to be publicly available, you cannot and should not be in the business of forcing users to use this browser or that. Do yourself, your users, and your webmasters a huge favor, and build with standards in mind. Feel free to ignore older browsers, but make every reasonable effort to support all modern standards compliant browsers.