I need to upgrade my hardware to Windows 10, can I still use my WATCHOUT keys version 4 or 5?
No. Windows 10 did not exist when WATCHOUT version 4 and 5 were discontinued, so there is no way version 4 or 5 could be adjusted for something that did not exist/a future version of Windows.
If you wish to stay with an older WATCHOUT version, but still update your hardware, you would need to stick with new hardware that can run with Windows 7. Windows 7 compatible hardware still exists, the hard part is finding new Windows 7 Pro licenses.
Otherwise you would need to upgrade to WATCHOUT 6.