Click on Apple logo at right top corner of the desktop.
Select system prefrences from the drop down list.
Select the network icon from there (the icon with silvered colour).
Now select the network which you want to connect either wifi, broadband or any other network.
Now click on advanced grey coloured button.
Now select the Using DHCP with manual address option from the drop down menu to the right of Configure IPv4.
Now enter the ip address you want to set.
Also enter subnet mask there.
By this your ip address will be change and now your all network working will have that ip address . You can also revert back the settings to automatic that will set your ip address that will be provided by your network