Overview
1. Add css link
Open index.html and, in the head section add this line:
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-+0n0xVW2eSR5OomGNYDnhzAbDsOXxcvSN1TPprVMTNDbiYZCxYbOOl7+AMvyTG2x" crossorigin="anonymous">
2. Add javascript link
Open index.html and, in the body section (after 'app-root') add this line:
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.1/dist/js/bootstrap.bundle.min.js" integrity="sha384-gtEjrD/SeCtmISkJkNUaaKMoLD0//ElJ19smozuHV6z3Iehds+3Ulb9Bn9Plx0x4" crossorigin="anonymous"></script>
3. Test
Serve project and open dev tools. Select 'Sources' tab and check that both css and javascript have been loaded.
Next
There are numerous changes in Bootstrap 5.