Originally Posted by avidflyer

Yes from the website:

Upgrades and Coupon Offers

Subject to vehicle availability, one-car-class upgrade is offered at participating Hertz locations in the U.S., Canada and participating European locations with a 2-hour advance reservation. Maximum upgrade is to a Premium car with a minimum reserved Mid-Size vehicle. For Compact 4-Door rentals, maximum upgrade will be to a Full-Size 4-Door car. Guaranteed upgrade is to the next car class only. This excludes Special Equipment such as Minivans, SUVs, Hertz Adrenaline CollectionŽ, Hertz Green Traveler Collection and Hertz Prestige Collection vehicles.

And yes, F is 2 classes over Intermediate:

A - economy
B - compact
C - intermediate/mid-size
D - standard
F - full size