Here are some hints to save your disk space
1. delete web stat
By default, three web statistic programs are running in cPanel (Webalizer, Analog and AwStats). Each of them has its log files store under folder. If you don't require them, feel free to delete files inside /tmp/Webablizer, /tmp/Analog or /tmp/AwStats, but keep the folder.
2. Set Default Address
Your default account could be stuffed with SPAM. Please set all unrouted email for your domain to "Discard with error to sender (at SMTP time)".
3. check mailbox usage
cPanel - Mail - Email Accounts - Usage / Quota / %
Please download them to your Outlook and delete them from the server. To delete emails from the server, please log in your webmail http://yourdomain/webmail
login with your email address and password.
4. check root directory
Some web files might upload wrongly to your root directory outside <public_html />. If this is the case, please FTP and delete them from the server. Your site will not be affected. Only web files inside<public_html /> count.