Computer genies please......help?

Whenever i uninstall a particular programme and then run the setup again the program finds its previous position . How could i delete everything about that program?My problem is that whenever i run the setup for mdownloader after uninstalling it in the add or remove programs it tells me that the trial time has expired (and it had expired a long time before). The progamme should have stored the data somewhere in my computer. how could i find it and delete it so that it can't put up the ugly message once again?