To increase Mailbox size on your email hosting plan please follow the steps provided below.
Log in to your Ozhosting control panel.
Click More Services under the Home tab, It will take you to the old Control Panel
Click on the "Exchange" tab
Click on email address you want to increase the mailbox size.
Click on "Limits"
On the bottom of the screen click on "Edit"
Edit the values for the following
Issue warning at xxx MB
Prohibit send at xxx MB
Size limit at xxx MB
Click on "Submit"
Click "Update Size"
Once submitted please allow up to 1 hour for changes to take effect on the server.