This article describes how to change the default Outlook data file on Windows 7 with Outlook 2010, but the steps will be very similar on earlier versions of Windows and Outlook.
Changing the default data file should not be required by most Outlook users. This should only be attempted by experienced users.
1. Click on Start (the Windows symbol) and then open the Control Panel.
2. Type "mail" into the search box at the top right of the Control Panel window and select "Mail" from the search results.
3. Click on the "Data Files..." button.
4. In the Account Settings window you can see the list of available data files as well as a checkmark indicating which data file is the current default. To change the default, select a different data file and then click on the "Set as Default" button.