Hello folks,
Root & Resellers can modify quota of an account from WHM. Below are the steps to modify quota.
1. Login to WHM using root/reseller's login details.
2. Click on Modify An account option, it will ask you to select an account that you wish to modify. Select it and click on modify button.
3. From here you can modify quota of that account. That's all.
Enjoy.... !! :)