Start VOCALOID4 Editor, select "Help" and then click "About VOCALOID4 Editor...".

In the displayed dialog box, check "System Ver".

If VOCALOID4 Editor cannot be started due to some problem, locate either of the following files to check the "Properties".

(1) If you are using a 32-bit PC:
C:/Program Files/VOCALOID4/Editor/VOCALOID4.exe

(2) If you are using a 64-bit PC:
C:/Program Files(x86)/VOCALOID4/Editor/VOCALOID4.exe

After selecting the file indicated above, right-click the file and select "Properties". On the "Details" tab, check the value for "Product version".