Yeah, I was wondering the same thing.
What do you mean when you say it was installed upside down.
I disagree zip.
The CPU and Hs will need to have the thermal paste cleaned off and reinstalled regardless of having been heated up.
Reason being, when you remove the heat sink it is going to leave an uneven covering of TIM on both surfaces.
Upon reassembling, this uneven covering can trap air bubbles that will act as an insulator between the CPU and Hs.
Use some acetone based nail polish cleaner or isopropyl alcohol (the higher percentage the better) and unused coffee filters to clean off the old TIM.
As you only need to use a small pea sized dot of TIM, you should still have plenty left over from the initial install.
Do not worry to much about getting a different TIM, it will not make to much of a difference (at most 2-3°c).