Options to downgrade?

Hello Simon. WPS v12.11 isn’t working perfectly for me. I’m finding some of the CSS customizations I made earlier and have relied upon for the past year have been “forgotten,” or something similar, in this new version, and it will need some tweaking. In the meantime, I need to get my site back up to normal looking order. I’d like to downgrade back to the previous version while I figure out what’s up. Is there a way I can do that?

http://ww.wp.xz.cn/extend/plugins/wp-symposium/