To install the latest V4 APK, follow the below procedure.
Download the Towelroot APK
Upload the APK to your Mobile device if it is on PC, Once the APK is on your Mobile, run the APK and install it.
After completing the installation successfully open the app and use it as required.
If your device is still not compatible with the latest Towelroot APK, I suggest you go with Rooting with Towelroot using Modstrings.The installation procedure for V5 APK is same. As a matter of fact, the procedure is same for any APK file. So, all you need to do is download the APK, install it and open the App for its compatibility. If it is compatible, you can root your phone in a couple minutes else use the mod strings.