HELP! directory permissions in Joomla with JumpBox

I am very new to JumpBox and Joomla (and PHP and MySQL).
I posted a query to Joomla administration discussion forums but it seems no reply yet.

In order to change its logo banner in the front page,
I need to upload or install my own banner and change the default one for the template (/var/data/joomla15/templates/rhuk_milkyway/css) with mine.

Media manager cannot access to the level of directory where the relevant file.
However, directory permissions are all writable but `\ ' and Log Directory ($log_path) /var/data/joomla15/logs/.
It seems I cannot change the unwritable status within Joomla.
So I changed Enable SSH/SFTP Logins to enabled.
But account settings only show a request to change email and password.

1. How do I use the command line?
2. Are there other easier and safer ways to install or upload the file where such a banner is used.

As I find VirtualBox is easier to use, I just want to solve this problem without switching to XAMPP.

I want to change directory permission from unwritable to writabl

I want to change directory permission from unwritable to writable
how can i do it.

thank you sangvan

Don't torture yourself

Don't know if this will help. I didn't want to learn SSH/SFTP so I installed a Joomla extension which gives directory and file access from the admin login. I use an extension called eXtplorer. Now I can create and edit files from a GUI file explorer interface.

I'll try to help

I'm under a deadline today, but I'll try to help you with this on Monday. I don't have a lot of experience with this myself. Before I give you a full answer, I'll check it for accuracy with my friends who are more experienced Linux CLI users than me. Help is on the way!