Beware : once you change the content of a torrent, you're not able to seed it anymore.
Open a finder window, search for all files named .dat
then just press cmd+a (select all) then cmd+backspace (delete) then cmd+backspace+maj (empty the bin)
#edit
You can also use gemini to find duplicates then delete itsthem with finderFinder, or if you're familiar with bash :
find -not -empty -type f -printf "%s\n" |
sort -rn |
uniq -d |
xargs -I{} -n1 find -type f -size {}c -print0 |
xargs -0 md5sum |
sort |
uniq -w32 --all-repeated=separate