Ah, under Display Settings > Section. Those are actually in the same order as listed in the Admicnp > vBulletin CMS > Section Manager. So, if you list them in the order you want them in the Section Manager, then they would show in that order when promoting a thread. It looks like the sections are set in packages/vbcms/content/section.php around line 1062-1104. So, you would need to modify that code there.