If you are using Internet Explorer you can set the default Search provider from the Tools>Manage Add-Ons menu. The Tools menu can be invoked by pressing the Alt X key combination.
If using Opera goto Tools>Preferences>Search to see a list of installed Search providers. Double click the one reuired as default and set the appropriate option.
If using Firefox, click the drop down arrow next to the currently active search engine icon and then select the alterante search engine that you want as default (you can see your current default search engine in bold). Firefox will remember your choice and use the selected search engine from now on (until you change it again).