Compress your Outlook PST file by using "Compact Now" feature of Microsoft Outlook. But, the size of your PST file is quite large so please don't take any risk with your important Outlook data files. I mean to say that you should go with any third party software. I would like to give you two better solution on the behalf of my personal experience. First is obviously Compress your PST file and the second one is PST Compact and Compress Tool.
Learn more info, here:- Compress Outlook PST Files.