mysql using high memory

i am runninf cpanel fro webhosting and about 20 account hosted, the most of them is new website with low traffict my memory usage is about 1GB of 4GB and CPU usage within 0.2 of 4cores based top/htop mysql usage is on top of chart: /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --user=mysql --log-error=/var/lib/mysql/my.hostname.nett.err --open-files-limit=10000 --pid-file=/var/lib/mysql/my.hostname.net.pid i'm using cpanel+cloudlinux with mariadb 10.0 and mysql governor by cloudlinux this is my mysql conf:
[mysqld] default-storage-engine=MyISAM innodb_file_per_table=1 performance-schema=0 max_allowed_packet=268435456 open_files_limit=10000

+------+--------------+-----------+--------------+---------+------+-------+------------------+----------+ | Id | User | Host | db | Command | Time | State | Info | Progress | +------+--------------+-----------+--------------+---------+------+-------+------------------+----------+ | 183 | eximstats | localhost | eximstats | Sleep | 378 | | | 0.000 | | 3259 | leechprotect | localhost | leechprotect | Sleep | 776 | | | 0.000 | | 3491 | root | localhost | | Query | 0 | init | show processlist | 0.000 | +------+--------------+-----------+--------------+---------+------+-------+------------------+----------+
how to reduce memory usage by mysql ?