Answer:
the distance between adjacent fringes is increased by a factor o 2
Step-by-step explanation:
To find how the distance between fringes is modified you can use the following formula for the calculation of the distance between fringes:

D: distance to the screen
d: distance between slits
λ: wavelength of the light
if d is decreased by a factor of 2, that is d'=1/2d, you have:

hence, the distance between adjacent fringes is increased by a factor o 2