Hello
On your current server apply a clear all totals and a rebuild to the database, then install 5.7 and to update the database use dm -u X:dbname.mbz5g2 -install.
Keep in mind to backup the database in your current server because you will delete all the history and sales details, so you can restore it later, or if you can do it in a virtual machine or in some test server it would be better.