When you're ready to delete a .pst file, exit from Outlook. Don't try to delete the file while Outlook is running.



For good measure, press Ctrl + Shift + Esc to bring up the "Task Manager," and check the processes to see if Outlook is running. It shouldn't be because you closed Outlook. But if at some point in the past, Outlook was not closed properly, there may be one (or more) extra instances of Outlook. Right-click on each extra instance and choose "End Task."


Then, using "File Manager," go to the drive and folder that contains the extra .pst file, and delete it.