SQL Guide : Using SQL for database administration : Managing user privileges and roles : Revoking privileges from a user or a role
  
Revoking privileges from a user or a role
REVOKE user_privilege ON table_name FROM username or role_name ;
The following example revokes the INSERT privilege on the table named TEST_TABLE from the GUEST_USERS role.
REVOKE INSERT ON TEST_TABLE FROM GUEST_USERS;
See also
Managing user privileges and roles