If you update the thumbnail and it gets aprroved it will show the updated thumbnail in the marketplace. But if you like (share) the item than the shared item show the first thumbnail not the new updated one.
Most of all, enjoy your time here. Thank you for being a valued Envato community member.
Format your entry with some basic HTML. Read the Full Details, or here is a refresher:
<strong></strong> to make things bold
<em></em> to emphasize
<ul><li> or <ol><li> to make lists
<h3> or <h4> to make headings
<pre></pre> for code blocks
<code></code> for a few words of code
<a></a> for links
<img> to paste in an image (it'll need to be hosted somewhere else though)
<blockquote></blockquote> to quote somebody
Complete List of Smiley Codes