[Ethereum] SyntaxError: Source file requires different compiler version

I am trying to compile the following contract on Remix IDE (online):
pragma solidity ^0.4.24;

contract ProofofExistence{
   event ProofCreated(
      uint256  indexed id,
      bytes32 documentHash);//an event can be listened by any client

   address public owner;//getters are already generated for public variables
   mapping  (uint => bytes32) hashesById;

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

   modifier noHashExistsYet(uint256 id) {
      require(hashesById[id] == "");
      _;
   }//The modifeir can be prepended to any function

   constructor() public {//constructor is executed when the contract s created 
      owner = msg.sender;
   }

   function notarizeHash(uint256 id, bytes32 documentHash) onlyOwner noHashExistsYet(id) public{
      hashesById[id] = documentHash;
      emit ProofCreated(id, documentHash);//Proof created event is emited to the block chain
   }//The core function of this contract allows its owner
   //to confirm a document id with a certain content

   function doesProofExist(uint256 id, bytes32 documentHash) public view returns (bool) {
      return hashesById[id] == documentHash;
   }//view/constant functions are read-only and do not cost gas
}

I am getting the following compilation error message:

browser/ProofofExistence.sol:1:1: SyntaxError: Source file requires
different compiler version (current compiler is
0.5.1+commit.c8a2cb62.Emscripten.clang – note that nightly builds are considered to be strictly less than the released version pragma
solidity ^0.4.24; ^———————-^

Can somebody please guide me how to fix this problem?

Zulfi.