Replace Syntax Error

Hello

In my database table I have replaced  <h3> Some Text </h3>  with <h2> Some Text </h2> in the Description column as below: 

UPDATE CAT_Products

SET Description = replace (Description, '</h3>', '</h2>')
WHERE Description <> '</h2>'

UPDATE CAT_Products
SET Description = replace (Description, '<h3>', '<h2>')
WHERE Description <> '<h2>'


However, when I try the same replace syntax code with the DescriptionHTML column in the same table, it does not work, e.g.

UPDATE CAT_Products
SET DescriptionHTML = replace (DescriptionHTML, ' &lt;h3&gt; ', '&lt;h2&gt;')
WHERE Description <> '&lt;h2&gt;'

What do I need to adjust?

Thanks