[evenmonkeys]

You have a couple of different options.

If you want to edit php files, it's in your forum/includes folder labeled "functions_editor.php" and you can search for "$editor_height" to find it. You'll have three options. Change the height respective to what you're using.

If you want to edit a template, you can open your "showthread_quickreply" template and search for "{$editor_height}" to find it. There are two options here again pending how it's being used. You'll want to replace them with the desired height.