To find out your Linux distribution, run

1:

plesk version | grep “OS version”

Or:

2:

cat /etc/*-release

Note: MySQL will not be upgraded on CentOS/RHEL-based operating systems if it was installed from the Webtatic Yum repository:

3:

rpm -qa | grep -i mysql
mysql55w-server-5.5.57-1.w6.x86_64

follow this link

https://support.plesk.com/hc/en-us/articles/213403429–How-to-upgrade-MySQL-5-5-to-5-6-5-7-or-MariaDB-5-5-to-10-x-on-Linux-