First of all let me say I do not think there is anything wrong with the new version as long as you're not upgrading. If its a new install on your site then it works fine. If you would like a copy of 6.2.3 till the bugs get worked out of the new version you can get it here.
You may have errors downgrading, such as headers already sent.
If you have access to your hosting you should have a file manager that allows you to Delete Plugins and Restore your site to a Previous Date. You should learn to use these features and also backup your data base via the hosting panel and not through a plugin.