How can I change the default browser? I need to change the default browser in my Android device to Opera. Is there any way to do that?
After installing Opera, when you open a link from somewhere in the system, you should see a popup asking you to choose between the browsers available. That popup should have a checkbox for saving the browser you choose as the default browser.

If you have already set a default browser, you must go to Settings > Applications > Manage applications, find the browser you now have as default and click on "Clear defaults" in the details page, then go through the process described in the first paragraph.