How to change a default application on Android
When you first try an alternative launcher or Web browser, Android asks if you'd like that application to be the default from now on. You may say yes and then come to regret it later on – perhaps you've decided you like another launcher better, or wish to go back to using the stock Android browser.
While you could always uninstall the application you no longer wish to be the default, that's a bit of a brute-force solution. Perhaps you still want it on your system, but only wish to use it every now and then.
To make an app stop being a "default application" for a certain type of action, do this:
1) Go to Settings > Applications > Manage applications.
2) Locate your application in the list. If the list is too long, you can hit the Running tab, because your app most likely is still running somewhere in the background.
3) Once you've located it, tap its name.
4) You will now find yourself in the Application info screen. Scroll down until you see the heading which says Launch by default.
5) Press the Clear defaults button, shown in the screenshot.
When you next try to perform the operation previously associated with this app (launch a browser, go to the home screen, etc.), you will be presented with a dialog letting you choose what app should be used. Presto!