アップデートできるスマートコントラクトを実装してみました ref: https://qiita.com/blueplanet/items/b639a90b44288eb29c9e

file0.txt

pragma solidity ^0.4.17;

contract InnerContract {
  function say() public pure returns (bytes32) {
    return "first ver";
  }
}

contract MyContract {
  address public owner;
  address public innerContractAddress;

  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  function MyContract() public {
    owner = msg.sender;
  }

  function say() public view returns (bytes32) {
    InnerContract innerContract = InnerContract(innerContractAddress);
    return innerContract.say();
  }

  function setInnerContract(address new_address) public onlyOwner {
    innerContractAddress = new_address;
  }
}

file1.txt

contract InnerContract {
  function say() public pure returns (bytes32) {
    return "second ver";
  }
}