As a normal ambassador you would, i say, never get a Pres upgrade.
Even as Royal it is more likely you win inthe lottery than getting upgrade to pres suite. There is no !!! guaranteed upgrade to a suite as ambassador.
You want it special...keep the pres suite booked directly and kindly ask for any benefit instead of upgrade. But if it is a special event honeymoon etc.
tell them, and im sure they will have a cake or bottle of free champagne
for you waiting in the suite. Always worked for me