The products you list run differently, so have very different startup instructions.
In the case of ftp, it runs under inetd (or xinetd in 10.2).
To enable or disable ftp under 10.1, edit the file /etc/inetd.conf and uncomment/comment the line that begins "ftp".
Then find the PID of the inetd process:
ps -aux|grep inetd
and kill -HUP <pid of inetd>
to make your changes active.
Under 10.2, the configurations are stored in /etc/xinetd.d
Edit the file 'ftp' and change te 'Disabled = yes' line to 'disabled = no'
then: killall -HUP xinetd
to make the changes take effect,
The above can be used for any x/inetd-based service.
DHCP, on the other hand, runs under its own process, not under inetd. As such it will have its own startup script. Once you find the script, you'll usually find that a:
/path/to/startupscript stop
followed by a:
/path/to/startupscript start
will restart the process (need to be run as root or under sudo, of course)