I have found that most FHR properties provide an upgrade if it is available, no need to be pesky with the staff. I rarely get more than one room class upgrade, however.

Sometimes, such as at the Trump Hotel in NYC, an upgrade is either a larger room or a better view. You need to say which you prefer when you book or check in.

If you stay at Mandarin hotels often, you should consider getting a Centurion card, as that gives you all of the FHR benefits plus one free night. If you use that feature often, it could pay for the whole card.