There is no automatic way to convert a Microsoft Outlook ANSI PST to a Unicode PST. Microsoft Outlook PST file supports Unicode and ANSI both files and then import items from the old data file to the new Microsoft Outlook Personal Folders PST.
1. Create a new data file.
2. Import items to the new data file.
Another way to Upgrade PST with the help of SysInfo PST Upgrade Tool. I can refer a link which can help you to upgrade your PST files:- Upgrade Outlook from Older to Newer.