If you are a Microsoft Office user and have an Office 365 subscription, you may update from Office 2013 to Office 2016 free of charge. Note, however, that if you wish to use Thai with your Office applications, you need to reinstall the "Editing Language" pack for Thai. To do this within any application click on "File", "Options", and "Language". Then, "Choose Editing Languages" at the top of the page and add Thai by clicking on "Add additional editing languages" if Thai does not show in the display box already. If Thai does show in the ball, click on "Install". The machine then downloads the Thai pack and adds it to Word, Excel, PowerPoint, etc.
Please let us know if you have any difficulty.
David in Houston