To start simply go to Pages > Home and edit it in Visual Composer.

Hover over the first 'Raw HTML' block and click on the pen icon to edit the block.

This is what the demo content looks like:

<h1>We help
<span id="typed-text">
    <span>Businesses succeed.</span>
    <span>Start-ups move forward.</span>
    <span>Entrepreneurs prosper.</span>
<span id="typed"></span>

You'll see the 3 changing text strings here between the span tags.

Be careful to just change the text and not delete any markup.

You can change the font size and color via - Appearance > Customize > Typography > Hero (Typed) Text: