Have an old OC site that I need to update to the newest

However I can't figure out my upgrade path because I can't figure out my version. I've tried to search for how to find my version but everyone just says it'll be in the footer of my admin login page, it isn't. Does this mean I'm running older than 1.4? I've tried searching this forum for how to find my version number but I can't find any useful results.
I apologize for such a silly question that must get asked all the time.

It means you're using OpenCart 1.4.7 or earlier. Unfortunately there's no easy way to tell what version that is without doing a source code comparison. I have old OpenCart versions available at http://legacy.opencarthelp.com along with their release dates if you want to give it a try (using something like your first order date or an old file creation date may help narrow the range down).

Upgrading a version that old (at least 4 years) could bring up a lot of issues so you may want to consider hiring a developer.

I'm thinking it's 1.4.0, looking at first order date was Feb/2010 and looking at index.php between 1.4.0 and 1.3.4 line 14 changes from:
// Load the application classes
to
// Application Classes

and I match the 1.4.0 file. Can I therefore assume that http://forum.opencart.com/viewtopic.php?f=2&t=50292
that script should work for me? Of course I'll do it in a test environment first but anything else I should look for?

It looks like it will work from the description. It's been so long since I've done a 1.4 to 1.5 upgrade I can't remember all the pitfalls. It's very likely your theme and all your mods will need to be upgraded so it's a good idea to have those ready to go before you start.

Thanks for the help, copied it all to a dev site and ran that update, had to install mcrypt and update some modules but it seems to be working. Although the new updates are pretty extensive and will have a big learning curve.

Glad to hear it's started off well.