the highscore table is in the savegame folder inside the install location
for example mine is in D:\GOG Games\Dungeon Hack\SAVEGAME

the files are hiscore.dat and hiscore.def
my suggestion is to makea new folder and move them into it and hope the game creates new hiscore files

if that don't work then copy them back and edit the copies in the savegame folder
and keep the copies in the new fokder just in case t0eh game wont recognise your edited versions

i hope that you can cleean up your scores list with this infos
btw i think that in the past i had done this mysef as a lets see what happens if i .... moment XD
anyroads goodluck friend and happy dungeonhacking

edit:
alterntiely i think teh newscore.exe file in the savegame folder resets the scores as well, you'd have to edit teh dosbox settings so as not to automaticily close the dosbox window when you exit the game o you can run it