sudo iptables -nL --line-numbers
Note: the -n means to not use DNS to resolve IP; the -L means to list rules; --line-numbers you can guess what it means.
Now you can choose a "chain", in this example: "INPUT" and use the "-D" to indicate delete and the final number is point to rule "5"
sudo iptables -D INPUT 5
You can also add a rule, and bellow I will use chain INPUT for a known hacker from Kenya, Africa:
sudo iptables -I INPUT 1 -s 126.96.36.199/16 -j DROP
That's it for now.
Cheers! and Shields up!