Find all files (type f) in the directory tree starting from the root directory (/) that have a depth between 2 and 4 (mindepth 2 and maxdepth 4), follow all symbolic links (follow), and do not have read permissions for all users (! -perm /444) and delete them (exec rm -f).
find / -mindepth 2 -maxdepth 4 -follow -type f ! -perm /444 -exec rm -f {} \;