Go to the employee record and switch to the Leave tab.
If you've not yet recorded any leave for the employee then you'll simply be told how many days they have remaining.
Once you start to record leave, the remaining days are shown differently.
The allowance is only reduced by adding leave that has the type "Holiday".
The number of days it's reduced by depends on how many working days are lost due to the holiday (as opposed to the total number of days taken).
Days that count as working days depend on the Working Pattern for the employee.