Before changing network settings, first check the active network interfaces with ifconfig:

eth0      Link encap:Ethernet  HWaddr b8:27:eb:1b:63:a8
        inet addr:192.168.1.6  Bcast:192.168.1.255  Mask:255.255.255.0
        inet6 addr: fe80::6502:67ff:89b:b2fd/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:43239 errors:0 dropped:24 overruns:0 frame:0
        TX packets:30644 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1000
        RX bytes:25068614 (23.9 MiB)  TX bytes:5993030 (5.7 MiB)

lo        Link encap:Local Loopback
        inet addr:127.0.0.1  Mask:255.0.0.0
        inet6 addr: ::1/128 Scope:Host
        UP LOOPBACK RUNNING  MTU:65536  Metric:1
        RX packets:1961 errors:0 dropped:0 overruns:0 frame:0
        TX packets:1961 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1
        RX bytes:160232 (156.4 KiB)  TX bytes:160232 (156.4 KiB)

From there, you can update the main network parameters one by one.

Set the IP address and subnet mask

Use ifconfig to assign the address and netmask to eth0:

ifconfig eth0 192.168.1.6 netmask 255.255.255.0

Set the default gateway

Add the gateway with route:

route add default gw 192.168.1.1

Change the network card MAC address

Bring the interface down first, modify the hardware address, and then bring it back up:

ifconfig eth0 down
ifconfig eth0 hw ether b877c322f8
ifconfig eth0 up

Configure DNS

One common way is to edit /etc/resolv.conf directly:

vi /etc/resolv.conf

nameserver 114.114.114.114
nameserver 114.114.115.115

After that, restart the network service to apply the changes:

service network restart

On newer Ubuntu versions, simply editing /etc/resolv.conf is no longer enough. In that case, the DNS settings need to be placed in the resolvconf configuration and then updated with the resolvconf command.

Edit the head file under /etc/resolvconf/resolv.conf/:

nameserver 114.114.114.114

Then refresh the configuration so it takes effect:

resolvconf -u