Step 1:
Open your client portal and click on your hosting account listed under YOUR ACTIVE PRODUCTS/SERVICE.
Step 2:
Click on EMAIL ACCOUNTS to be taken to your cPanel.
Step 3:
Click on QUOTA for ther email account you want to change the quota for.
Step 4:
Adjust the quoata for the account and click the Save/Quota button.
Step 5:
You're done.