Renew my ip address (dhclient not found)

If it's installed, dhclient would be in /sbin, which normally is not in your user path. If you do

sudo su -

then your path would have that directory:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

However, ifconfig also lives in that directory, so it seems likely you do not have that installed. The package (if you have a CD for installing...) is isc-dhcp-client