I needed today to remove duplicate files from a big folder (8Gb+, 10000+ files). I use the nice fdupes program written by Adrian Lopez
fdupes -rdN .
Note the point after the parameters. That means to search inside the current folder. A path could be provided instead of it. The options are:
-rmeans search recursively
-dmeans delete. use carefully and read the man page to understand what could go wrong!
-Nmeans “no prompt”, i.e. the program will not ask which file to keep when multiple are found (I didn’t care, you might)