You can remove previously granted permissions with the zfs unallow command.
For example, assume that you delegated create, destroy, mount, and snapshot permissions as follows:
| # zfs allow cindys create,destroy,mount,snapshot tank/cindys
# zfs allow tank/cindys
-------------------------------------------------------------
Local+Descendent permissions on (tank/cindys)
        user cindys create,destroy,mount,snapshot
------------------------------------------------------------- | 
To remove these permissions, you would need to use syntax similar to the following:
| # zfs unallow cindys tank/cindys # zfs allow tank/cindys |