Answer:
-Reduce the mass of the earth to one-fourth its normal value.
-Reduce the mass of the sun to one-fourth its normal value.
-Reduce the mass of the earth to one-half its normal value and the mass of the sun to one-half its normal value.
Explanation:
The force (F) between two massive bodies (earth-sun system) is given by the following equation:
Where "g" is the gravitational constant "Me" is Earth's mass, "Ms" is the Sun's mass and "r" is the separation between the Earth and the Sun.
1-) If we reduce the mass of the earth to one-fourth its normal value:

2-) Reduce the mass of the sun to one-fourth its normal value.

3-) Reduce the mass of the earth to one-half its normal value and the mass of the sun to one-half its normal value.

4-) Increase the separation between the earth and the sun to four times its normal value.
.
Therefore, changes 1, 2 and 3 would reduce the magnitude of the force between them to one-fourth of the original value.