You can fill in all these resources according to your requirements, an example input can be:
Disk Space: 100
FTP Accounts: 10
Note: 0 is considered unlimited.
If you feel the need to modify the parameters for existing package you can do so via modify package page.
From the list select the package you want to modify and it will fetch the current parameters for the package, once you are satisfied with new parameters you can click “Modify Package”.