How do I remove the passphrase for the SSH key without having to create a new key? [closed]

$ ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]

if [ -f ~/.agent.env ] ; then
    . ~/.agent.env > /dev/null
if ! kill -0 $SSH_AGENT_PID > /dev/null 2>&1; then
    echo "Stale agent file found. Spawning new agent… "
    eval `ssh-agent | tee ~/.agent.env`
    ssh-add
fi
else
    echo "Starting ssh-agent"
    eval `ssh-agent | tee ~/.agent.env`
    ssh-add
fi

ssh-copy-id -i ~/.ssh/id_dsa.pub username@host