The file name that you specify for an Outlook Data File (.pst) appears in the folder pane. Prior to Microsoft Outlook 2010, the default display name for Outlook Data Files (.pst) was Personal Folders. This can be confusing if you work with multiple Outlook Data Files (.pst) that were created in previous versions of Outlook. We recommend that you use a descriptive display name for each Outlook Data File (.pst).
Click the File tab.
Click Account Settings, and then click Account Settings.
On the Data Files tab, click the Outlook Data File (.pst) file, and then click Settings.
In the Name box, enter a descriptive name for the Outlook Data File (.pst).
Changing the display name doesn’t rename the file. Only the name as it appears in the Folder Pane is changed.