Plesk 11.5 to 12.5 fails: "depsolving problems"

My hosts are trying to upgrade my managed server from Plesk 11.5 to Plesk 12.5, but they tell me it is failing with the following error messages, which they say is due to me "upgrading MySQL using the atomic repository". I have no idea what that means, I wouldn't know how to do it, but is there a solution:

--> Missing Dependency: real-mysql = 5.5.33-20.el5.art is needed by package mysql-server-5.5.33-20.el5.art.i386 (installed)
mysql-server-5.5.47-1.el5.remi.x86_64 from...

Plesk 11.5 to 12.5 fails: "depsolving problems"