Need to find out if our org is using SOAP API legacy versions:1.8, 2, 2.2, 2.5, 3, 4, 5 and 6

I have gone through the steps SF has advised in their email using Workbench, but I still could not get or find the info needed to find this out.

Please help! Does anyone have a step by step guide on how to do this?

Thanks!