help with root for MTK6582

[trex]

Hello I rooted my gsm with vroot 1.6, but then I've uninstalled the chinese superuser app, and now it seems the phone is not rooted anymore. So i tried again to root it, but it seems a new version of vroot is out 1.7.2 and it seems to work, or at least does not give any error, but at the end the phone is not rooted and this chinese super user app is not installed at all. What I am missing? I've uninstalled vroot, and downloaded 1.5 version, but it seems that the PC has downloaded some upgrade files somewhere, and when I start Vroot, it says that it is version 1.7.2.
What to do now to root the device?