The way I do it, which may be the long way
as root, or sudo all commands:
ifconfig eth0 down
dhcpcd stop << if this doesn't work, kill -9 process id
rm /var/log/dhcpcd****.pid
dhcpcd eth0
there's probably an easier way, and I think
ifconfig eth0 down
ifconfig eth0 up
should work, but I've been having probs with my install lately
edit... Just saw MasterC's post, and the reason I kill dhcpcd, is that I get dhcpcd already running when trying a dhcpcd eth0 right away. Of course, this could just be me