Microsoft Outlook is a well-known email managing client that is often referred to as Outlook. Outlook manages email, contacts, and calendars among other things. A PST file refers to personal storage. In this case, the files store the information for your contacts, old emails, and calendar updates. If you want to delete a PST from Outlook you can do so very easily from the open application.
Select "Start">"Programs">"Microsoft Office">"Microsoft Office Outlook" to open the application.
Right click on the personal folder that you wish to delete on the left side of the application under "Personal Folders."
Select "Close Personal Folders" from the pop-up menu to completely remove the PST.