how long does it take for fuel to go bad if the car has been sat for months?

if i've got a non runner, how long does it take for the fuel to go bad?

i've got a nissan almera and it run for a few minutes then cut out, its been sat still for around 6 months and i've only just purchased it, it was running and it either stalled or cut out.

do i need a new fuel filter or just to drain the current fuel and put in fresh fuel?