Question: How can increasing the radius of earth may cause an impact on the solar system ? Like, would earth may start making a bigger orbit (due to increase in size and wait) or vice versa ? or else ?

PS: The base of my question arises from the point of view of "Growing Population", and managing it by "artificially increasing the size of earth" (Instead of say, finding possibilities to live on other planets like Mars). So, if the radius increases, naturally the circumference of the sphere, and hence surface to live on will increase.

I understand however that probably exploring newer planets might be more feasible solution. But just for curiosity I shared my query. :)

Answer: 
Radius has little to do with an object's orbital properties. Instead, consider its mass.

The mass of a satellite (in this case the Earth) does not affect any properties of its orbit. This makes sense, since the force of gravity is proportional to mass, and acceleration is proportional to force divided by mass. Therefore, the Earth's orbit would not change.

The moon's orbit, however, might. If one were to double the central mass of a body being orbited, the velocity of the orbit would increase by a factor of sqrt(2), causing the period of the moon's orbit to reduce to around 20 days. Also, the moon's orbital radius would decrease, thereby increasing tides slightly.

All and all, there would be few notable changes.
Increasing the radius does not require new matter.

See Menger sponge as a conceptual model; and assume that when pieces of Earth are removed from its surface (excavation for raw materials) and then placed in a vertical order (buildings), Earth's surface takes a less dense form.
If Earth's surface were hypothetically covered by tall buildings. Earth's radius would have increased by the height of the buildings, but its surface mass would also be less dense.

Therefore now the question becomes: How much of Earth's mass can be tampered with by reducing its density, before Earth's ecosystem becomes too risky for its habitants?
Maybe that would help estimate a more realistic maximum sustainable human population.

\*As per the Menger sponge, less density may translate into more surface area for habitants.