There are a few ways. What you are referring to is CHMOD. Any good
FTP client will let you do it, or you can telnet or
ssh into your server and cd to the directory and do chmod <filename> 755, 777 etc etc...
i.e. chmod 777 /username/public_html/images/ or cd /username/public_html/images/ then chmod 755 foo.jpg
As for perl, what you have is generally the default path to it and usually remains unchanged.