The Boeing 737-500 has six emergency exits: two at the front, two at the rear and two overwing exits...
Apologies if the answer sounds obtuse - I'm not quite sure what it is you're asking.
Chances of an upgrade are very good on LGW short haul routes - it may be available via Manage By Booking on BA.com or failing that at the check-in. BA accepts all popular credit and debit cards.