Replace parent element with its contents

I'm trying to do something similar/same as in this question: How to remove only the parent element and not its child elements in JavaScript?

<div>
    This is some text here
    <h2>This is more text</h2>
</div>

All I want is to remove the H2 tag. The result should be:

<div>
    This is some text here
    This is more text
</div>

Assume that I have the H2 element already:

if (parentElement.nodeName.toLowerCase() == "h2") {
    //now what? I basically want to this: $.replaceWith(parentElement.innerText)
    //just without jQuery
}