CentOS 7 /dev/mapper/centos-root at 99% use Disk Full

My Disk storage is almost full when I checked in the server [root@vps ~]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 908M 0 908M 0% /dev tmpfs 920M 0 920M 0% /dev/shm tmpfs 920M 18M 902M 2% /run tmpfs 920M 0 920M 0% /sys/fs/cgroup /dev/mapper/centos-root 35G 27G 8.2G 77% / /dev/sda1 1014M 229M 786M 23% /boot /dev/mapper/centos-tmp 3.0G 82M 3.0G 3% /tmp tmpfs 184M 0 184M 0% /run/user/0
How do I Cleare the /dev/mapper/centos-root/ unwanted memory Its just a basic blog site with some images not more than 10gb Am new to handling server expecting answers in simple terms [root@vps ~]# du -a |sort -n -r| head -n 20 172096 . 163564 ./postfix-3.2.0 90780 ./postfix-3.2.0/src 38680 ./postfix-3.2.0/libexec 15228 ./postfix-3.2.0/bin 7840 ./postfix-3.2.0/src/util 7760 ./postfix-3.2.0/src/global 6896 ./postfix-3.2.0/lib 5448 ./postfix-3.2.0/src/smtpd 4664 ./postfix-3.2.0/src/smtp 3708 ./postfix-3.2.0/src/cleanup 3492 ./postfix-3.2.0/html 3400 ./maldetect-1.6 3284 ./maldetect-1.6/files 3212 ./postfix-3.2.0/src/tls 3164 ./alldb_before_ugrade.sql 3080 ./maldetect-1.6/files/sigs 2884 ./postfix-3.2.0/src/smtpd/smtpd 2884 ./postfix-3.2.0/libexec/smtpd 2740 ./postfix-3.2.0/src/postconf [root@vps ~]#