function acraCleanup() {
  var SPREADSHEET_KEY = "BBBBBV9AAAAAAGJGZVQ0Z2M0WnFDSAFAGACWFUMUE";

// Replace with your spreadsheet Key,

//you can find this by trying to share the Spread sheet

// and getting the key between the "=" and the "&"
  var SHEET_NAME = "Sheet1"; //Sheet1 unless you changed sheet name
  var rowsToKeep = 1000; //Will keep bottom 1000 Rows
  var sheet  = SpreadsheetApp.openById(SPREADSHEET_KEY).getSheetByName(SHEET_NAME);
  var rows = sheet.getLastRow();
  var numToDelete = rows - rowsToKeep - 1;
  if (numToDelete > 0) sheet.deleteRows(2, numToDelete);
}