How to explicitly drop dynamic network connection in favor of static one?

[Danny Colligan]

I am running a FTP server that is capable of grabbing both a dynamic
and static IP address.  Because of various circumstances regarding the
building's networking, I wanted to switch from the DHCP-given address
to a static one.  Therefore, I changed the entries in
/etc/networks/interfaces to reflect the static values and did a sudo
/etc/init.d/networking restart.  This, however, did not make the
server drop the dynamic connection.  I eventually accomplished this by
the Windows universal solution (i.e. a reboot) and then the server
used the static address.

My question is, what would be the "right way" to do this?  That is,
explicitly drop the DHCP connection in favor of the static one without
rebooting?

Thanks in advance,

Danny Colligan