String fileName = Environment.getExternalStorageDirectory() + "/myApp.apk";
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.parse("file://" + filePath),"application/vnd.android.package-archive");

//intent.setDataAndType(Uri.fromFile(new File(fileName)), "application/vnd.android.package-archive");
startActivity(intent);

Intent intent = new Intent();
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setAction(android.content.Intent.ACTION_VIEW);
/* 調用getMIMEType()來取得MimeType */
String type = getMIMEType(f);
/* 設置intent的file與MimeType */
intent.setDataAndType(Uri.fromFile(f),type);
startActivity(intent);

<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.INSTALL_PACKAGES"></uses-permission>
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

Uri packageURI = Uri.parse("package:com.android.myapp");
Intent uninstallIntent = new Intent(Intent.ACTION_DELETE, packageURI);
startActivity(uninstallIntent);