Where the ipaddr option defines the static IP address you want.
Then run /etc/init.d/network restart to apply the changes.
Do a ifconfig to confirm that it worked, you should see a bunch of lines but these are the ones you're interested in:
wlan0 Link encap:Ethernet HWaddr 40:A3:6B:C1:18:C3
inet addr:192.168.1.145 Bcast:255.255.255.255 Mask:255.255.255.255
If you see your address from above, you're all good.
Using Your Router
In the off chance that the above doesn't work:
You'll have to log into your router configuration page, point your browser to 192.168.1.1, there will usually be a username and password prompt. Google your router for the login info.
In the menus there will should be some sort of DHCP or Static IP Address options, but its very router specific.
The Omega method worked for me, so I'm hoping it will for you as well.
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