If you want to change the email quota from cPanel, follow the steps given below.
1) Log in to cPanel.
2) Go to the section Mail >> Email Accounts.
3) Click the Change Quota button to the right of an email address for which you would like to change the Mailbox quota for.
4) Set the new Mailbox quota value in the box. [By default it will be 250MB].
5) You can also set this value as “Unlimited” by checking the option “Unlimited”.
6) Click Change Quota button.
Your email quota has been changed successfully.