> I've just downloaded a big file (10Mb) with other program
> (p.e. Filehound) nad I don't wand to download it another 
time.

See in 'Set Options' / 'Scan rules' ; example:
-*thisbigfilename.zip

(don't forget the * between - and thisbigfilename.zip)

You can also decide to exclude all files bigger than 10MiB 
(10000KiB)

-*[>10000]