Do you want to upgrade Outlook PST files to get maximum size limit? Or, do you want downgrade the PST files to make them openable in the older versions? To upgrade Outlook PST files, you need to convert them from ANSI to Unicode format; and to downgrade them, you need to convert them from Unicode to ANSI format. SysInfoTools PST Upgrade & Downgrade is an advanced solution to perform PST files conversion, i.e. ANSI to Unicode and Unicode to ANSI.