find .  -type f -print0 | xargs -0n 1 bash -c \
's=$(dirname "$0")/$(basename "$0"); 
d=$(dirname "$0")/$(basename "$0"|tr "[A-Z]" "[a-z]"); mv -f "$s" "$d"'

while IFS='' read -rd '' dname; do  mv "$dname" "${dname,,}";  done < <( find . -depth -type d -print0 )