You may want to connect your Mac to a different network than the one it connects to by default for reasons like greater strength, faster speeds, security etc. This tutorial shows you how to change the default wi-fi network order in just a few minutes.
Normally, people delete certain networks to gain access to the preferred one. However, you don’t have to do it in case you have multiple wi-fi networks at your home by modifying the list of Preferred Networks.
This tutorial was tested to work on all Macs running Snow Leopard including Macbook, Macbook Pro and iMacs.
I ran into this problem when I purchased a new Belkin N+ router. My Mac would by default connect to my older router at startup and it was tiring to change networks every time, until I found this simple fix.
Steps to Configure Order of Wireless Networks:
Launch System Preferences.
Select Network and then under AirPort click on Advanced.
As you can see, here under the AirPort tab there is a list called Preferred Networks.
Currently, my Mac lists my iPhone 4′s Personal Hotspot at the top and my new Belkin router at the last. You can just drag the networks to change the order.
In case the first one is missing, your Mac will automatically connect to the network next in the list. Here’s what my reconfigured wifi network order looks like.