How switch between Ethernet and WiFi?

Hello,

I have a notebook computer running Windows 7/Internet Explorer 7 which, at home, I have connected by Ethernet to my router. This works well and I have no desire to change things.
But I also need tyo be abale to connect by wi-fi when I am away from home and want to check emails etc.. But although my computer has wi-fi capability, IE tells me it cannot connect to the internet.
This, I understand is because the machine has been set up so my default Internet connection is via Ethernet.
How do I set it up so I can easily select bethween Ethernet at home and wi-fi when away?
I'm certain it can be done, but I don't know enough to start fiddling with the settings on my computer and risk losing everything.

Any help will be greatly appreciated.
PatM