1) Login to the server as root user
2) Use the commands given below
iptables -D INPUT -p all -s IP.ADDRESS.HERE -j DROP
iptables -D OUTPUT -p all -s IP.ADDRESS.HERE -j DROP
After executing the above commands, you should be able to remove the IP address
you wish from the list of banned IP addresses.
3) Save and restart the IP tables service by using the commands given below
service iptables save
service iptables restart