Go to
Cydia, press the installed app, press on
Filesystem Content, note the installed files and remove them using
iFile or an SSH program like
WinSCP. Make sure you delete
only these files,
nothing else, otherwise you might go in trouble.
Reboot. Back on Cydia and check if it is still installed. If so, press
uninstall now (
this doesn't always happen to leave the uninstall option in Cydia). The program icon should be gone now. I repeat:
Don't delete any other file, you might brick you iDevice,
don't blame me if you do.