'G' is representation for Gravitational constant, by definition it is universal constant, it does not change.
'g' on the other hand is used for acceleration due to gravity. Never write it as G, it is always in miniscule. g force is given by the formula
g = G*m/r,
just put in the values of G (6.6742 x 10^-11 m3 kg-1 s-2), mass of sun (1.9891×10^30 kg) and radius of sun (1.392×10^6 km).
Where ^ means, raised to the power.
I'd love to solve it for you but I am not sure it might be your homework.
Anyway, do let me know what the answer is.