Verify if MariaDB 10.1 is installed

rpm -qa|grep -i maria|grep "\-10.1."

Upgrade

service mysql stop
service mariadb stop
systemctl disable mariadb
rpm --nodeps -ev MariaDB-server
yum -y install MariaDB-server
yum -y update "MariaDB-*"
systemctl enable mariadb
service mariadb start
mysql_upgrade

Check for the custom configuration

diff -Bw /etc/my.cnf.d/server.cnf.rpmsave /etc/my.cnf.d/server.cnf

Verify upgraded packages

rpm -qa|grep -i maria|grep "\-10.2."

The output should look like this

MariaDB-compat-10.2.36-1.el7.centos.x86_64
MariaDB-server-10.2.36-1.el7.centos.x86_64
MariaDB-common-10.2.36-1.el7.centos.x86_64
MariaDB-shared-10.2.36-1.el7.centos.x86_64
MariaDB-client-10.2.36-1.el7.centos.x86_64