Before starting to change the tensions, write down (or take a picture of) the settings you are starting with.
That way one has a starting point to refer to.
I don't know about setting/changing the tensions on newer machines, but on my older Pfaffs (1471 and 1473) - the technician told me to thread it on the "second thread" path to help with tension issues because the tension discs were worn on the "first thread" path.