Code

function myFunction() {
  var testDate = new Date();
  var secondDate = new Date();
  secondDate.setHours(testDate.getHours()+6);

  var date = Utilities.formatDate(secondDate, "GMT+9", "yyyyMMdd");
  Logger.log(secondDate)
  var updateFileId = "File_ID";
  var imageURL = "https://smtgvs.weathernews.jp/s/forecast/img25/JAPAN."+date+".png";

  //get image
  var image=UrlFetchApp.fetch(imageURL).getBlob();
  


  //update image
  updateFileById(DriveApp.getFileById(updateFileId).getName(),updateFileId,image);
}
  

//Update Blob
function updateFileById(title,id,blob) {
  var body = {
    title: title ,
    mimeType: 'video/mp4'

  };
  file = Drive.Files.update(body,id, blob);
}

var files = DriveApp.getFolderById("Drive_Folder_ID").getFiles();
while(files.hasNext()){
   file = files.next();
 }