Updating latest version - lost file upload button
But if you need to roll back try this:
In config folder/site.php
At the end of Password_Salt line take out
<?php define('DIRNAME_APP_UPDATED', 'concrete5.4.2');?>
If you're using 5.4.2 or whatever one you have in there.
There are other things you could try, but see if the one above helps.