var AdmZip = require('adm-zip');

//create a zip object to hold the new zip files
var newZip = new AdmZip();

// reading archives
var zip = new AdmZip('somePath/download.zip');
var zipEntries = zip.getEntries(); // an array of ZipEntry records

zipEntries.forEach(function(zipEntry) {
    var fileName = zipEntry.entryName;
    var fileContent = zip.readAsText(fileName)
    //Here remove the top level directory
    var newFileName = fileName.substring(fileName.indexOf("/") + 1);

    newZip.addFile(newFileName, fileContent, '', 0644 << 16);        
});

newZip.writeZip('somePath/upload.zip');  //write the new zip