Aa757first: You better go with B747Skipper on this one. Some of these other answers have some bad info. First, the 100, 200 and SP
have the small door on the right (and sometimes left) side of the upper deck. This is called the Crew Entry Service Door (AMM 52-23-00). It is located at station 405. It is 24 x 48 inches. It is aft of the P6
panel, and forward of the forward wall of the lav (in most standard configurations). It is not in the cockpit. It is accessible to the passengers on the upper deck. Those passengers should exit down the stairwell, and out a main deck door. If that route is not available, they could exit down the slide from the crew entry service door. There are no slides or opening windows in the cockpit.
The aircraft with the 280 inch upper deck (the 300 and 400 models, and 200 models with the mod) do not have the Crew Entry Service Door (in most standard configurations). They have a left and right Upper Deck Door (AMM 52-23-00) at station 666-714. It is 42 x 72 inches. They are equipped with slides. Depending on your airlines operations, passengers may go down the stairwell and out the main deck doors, or exit out through the Upper Deck Doors in an emergency.
All 747's have the emergency exit hatch in the ceiling of the cockpit. It is called the Crew Compartment Overhead Hatch (AMM 52-21-00). It is for the emergency egress of the crew, and not intended for use by the passengers. It is just left of centerline, almost directly above the First Observers seat. Adjacent to the Overhead Hatch in the ceiling, are from 5 to 8 emergency descent devices. These are handles attached to an inertial reel. As the crew exits through the hatch, they will grip the handles and the inertia device (friction brake) will lower them over the side to the ground. The device does not reel back up, rather it remains extended until reset by maintenance.
Hope you find this interesting. Regards,