find top-folder -type f -name "'.DS_Store"DS_Store' -exec rm -f {} + or, more simply,
find top-folder -type f -name "'.DS_Store"DS_Store' -delete where top-folder is the path to the top folder you'd like to look under.
To print out the paths of the found files before they get deleted:
find top-folder -type f -name "'.DS_Store"DS_Store' -print -exec rm -f {} +