Depending on your theme, you should look into the header.php file. In there you’ll see something like:
<div class=”search”><?php search_form(); ?></div>
Remove this to get rid of the search form. You can also do this through css (recommended for upgrading) by setting the display: none; property.
To be clear, that just removes the search box, or hides it from display if you choose to do it with CSS
display:none;. People could still access the search function directly by accessing the URL
http://www.example.com/bbpress/search.php?q=keyword. If you just want to reduce visual clutter, remove the code from your template as suggested by hatter.
i mean disable but not “unshow”