To answer the OP's original question...

On Microsoft site the instructions are to Download the Tool and select Run (no saving to the PC). Is there a reason for saving it to the PC first as suggested on TenForums?
It actually makes no difference if you download the MCT and run it from the PC, or run it direct from the Microsoft site. But here on TenForums we prefer to have the MCT handy in case we need to run it again, we also prefer to use its 'make media for another PC' to make install media (as an ISO or USB) and use that to upgrade or install. Microsoft's preferred method is to run the MCT to 'upgrade this PC now'.

Both work, but the TenForums way leaves you with the install media to use again, either on another machine, or to try again on the same one if there was a problem. Microsoft's way means you would have to download all the install files again if you needed to repeat the exercise.