rem is for removing an IPv6 address from the interface.
regular IP addressing that most of us use is IPv4 or just called IP
for more info on IPv6 see:
IPv6 is new IP addressing using 128 bits , instead of 32 bits.
to change the IP address it is bound to just type
ifconfig eth0 <new ip address>
ifconfig eth0 address <new ip address>
To remove the interface just type
ifconfig eth0 down
To bring the interface back
ifconfig eth0 up
The settings you make with ifconfig will not be saved if you reboot.