I think the unfortunate answer here is, you can't using just Construct. Version numbers are the domain of subversioning software. You would need to create a subversion server (or setup a GitHub account), save your project as a folder instead of a single file, then use a subversion program to commit the project. This will create a file in your project that records the current version being worked on. In the game you would then have to reference that file to get and display the version number.
If that seems like too much work, the easiest thing to do is use a global variable that stores the version and after exporting a version to upload, update the version number. I say AFTER, not BEFORE because I know I am more likely to remember after I export. In which case, I would facepalm, update and re-export. If I export then update, I can immediately update the number so the next export version is ready for the next time.
On a side note, subversioning is a great idea because it usually gives tons of options for rolling back problems. If you haven't ever looked into it, you should.