1) Click on
Services in your Customer Zone

https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/33025198926/original/agzJW6trSL9-otT7-FUGU3BuYJLTLA4FUQ.png?1557231903

2) Click on
Manage Product next to the service you wish to access.

https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/33025198935/original/jjEcxxa4ugdwUOV2XZEobxBUlSq9d0Felw.png?1557231909

3) Finally, click on Login to Control Panel to access your domain management interface.

https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/33025198937/original/fmYksfkRAjaM4U2zWA20gNoyvDzcR7nfEw.png?1557231914

4) Click on
Mail and Accounts

5) Click on the
email account

6) Enter the desired limit in MB