Windows version: type "About" in the search bar at the left bottom of the screen
Microsoft Office version (check out here how to find out the bit version of your MS Office): launch Microsoft Excel, Word, Powerpoint or Outlook.
Go to File/Account:
JChem for Office version: press "About" on JChem tab in Excel, Word, Powerpoint or Outlook
The bit version of your Microsoft Office is also important, you can find the steps how to check it on your computer here.