I logged in into our cpanel to view phpMyAdmin but I can't open it. It give me this error message:

Warning: session_write_close() [function.session-write-close]: write failed: No space left on device (28) in /usr/local/cpanel/base/3rdparty/phpMyAdmin/index.php on line 42

Warning: session_write_close() [function.session-write-close]: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/cpanel/userhomes/cpanelphpmyadmin/sessions) in /usr/local/cpanel/base/3rdparty/phpMyAdmin/index.php on line 42

Warning: Cannot modify header information - headers already sent by (output started at /usr/local/cpanel/base/3rdparty/phpMyAdmin/index.php:42) in /usr/local/cpanel/base/3rdparty/phpMyAdmin/index.php on line 99

I contacted the support to assist me with. They just told me that the server is unmanaged. They told me to delete the free the partition but I don't know how to do it. I'm noob on that matter. The /var/log/btmp is over 8GB as they said. I want to delete that file.

How would I do this?

I need to free the space of the partition. I need some steps on how to do it and also steps on how to delete the /var/log/btmp.

I have been googling around but I haven't found anything.