Files such as that one, you don't really 'edit', rather you echo stuff into them and it 'sticks' (for example you would echo a 0 or a 1 for false or true respectively, or you might echo a yes or a no into it, or some other thing, depending on exactly what file, and for what subsystem, you're changing.).. For example:
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
That means "icmp_echo_ignore_broadcasts = TRUE", so it will ignore them.
Note that only root can usually write to such files.