fdupes is a program for identifying/deleting duplicate files residing within specified directories.
How I typically use it to find duplicate files
fdupes -r -n -1 -S /path/of/directory/to/search/for/dups
How I typically use it to delete duplicate files. It will prompt you for which file to delete. You can preserve multiple files by using a comma separated list of values. See documentation for caveats.
fdupes -r -n -1 -S -d /path/of/directory/to/search/for/dups