This is probably the recommended steps to follow to upgrade.
- Install the new version of Linux Mint
- Install Apache package
- Install MySQL package
- Install PHP package
- Install Pure-FTPd package
- FTP files (using shell or bash script). The backup area of this tutorial has the example script.
- Rebuild MySQL users, priviledges, pound out bind-address, rebuild databases, tables, data.
- Change the private IP address in the PHP files that make a call to MySQL.