Plesk is a powerful control panel that can be used to resell web hosting - and due to this, you can specify quota limits per subscription so that each client can be allocated certain resources. They can be defined per website/subscription. To change these, you will need to follow these steps:

1. Login to your Plesk Control Panel.

2. Once logged in to Plesk, click on Subscriptions, then click on the relevant subscription for the site you want to change the settings for.

3. Click on 'Customize'.

4. You'll now be at the page where you can specify limits for the subscription or set them to unlimited.

5. Another setting to take note of is right at the bottom of the page - the Subscription Expiration Date - this is commonly used by resellers to expire the hosting after a set period of time. This will stop any sites and mailboxes from functioning on the server - so if it is not required, set it to Unlimited.

6. Once complete - click 'Update & Lock' to save your changes.