You can create a cash distribution from the estate account in 2 ways:
When defining a cash distribution, you will see "Available" and "Planned" amounts at the top of the Distribution dialog. These amounts show you the balance currently available in the Cashflow estate account for this distribution, and the balance planned to be available once all defined future distributions have been made.
You can define a cash distribution that exceeds either or both of these amounts, since you may be aware of future expected deposits: these numbers are presented only to help inform your plans.
Note that if you have an asset of type "Cash" (and it is therefore NOT the estate account), you should deal with it like any other asset, including defining related asset distributions.
See also Manage Distributions.