Note: Your control panel may look slightly different depending on the theme you are using, however the steps will be the same for all themes based off of the X3 theme.
How to view your hosting accounts disk space usage:
Login to cPanel, and under Files, click Disk Space Usage.
This page shows you where disk space usage is distributed within your account's home directory. It can be useful when you need to know what is causing you to reach a disk space quota.