If you give me cpanel, then there is definatly downgrade option. so i will revert back to 5.6.
I have 7 years of experience in PHP, Codeigniter, Yii and MySql.
If you want to keep the version 7.X, then there is nees to also upgrade the oscommerce plugin, that will may be create problem, because all of the plugin is not updated by 7.X php