"So where do I look please?"
Click Start - Run - Type "msconfig" (without quotes) under BOOT tab you should see something like this -
Windows 7(C:Windows):Current OS; Default OS
- that is the "active" version you refer to.
If another OS is listed it will show and that is the one you can choose to safely delete.
**Note Wndows 7 referred to above is what mine looks like** - yours will refer to your OS