Changing the TTL is a fairly uncommon task, but if you're sure you want to do it, you can viasysctl
sysctl -w net.inet.ip.ttl=64
(or whatever value you prefer).
Changes made viasysctlare transient, and lost when you reboot. If you want the change to be persistent, add the 'variable=value' to /etc/sysctl.conf
