Trace all files for an application....

I had a trial version of an application.
It gives you a 7 day temporary licence.
I didn't have time to preview it when I installed it and the temp licence expired.
I want and will have time to preview it this weekend.
Can anyone tell me how to completely uninstall an application so I can re-use the temp licence.
The programme wont let me use a temp licence even after I un-install and re-install for obvious reasons.
However it is a genuine attempt at previewing the application.

Thanks,

Johnny