When you add a new employee their default payment options - including amount and frequency - are copied from the Default Pay Options that are set for the Employer.
To edit these defaults click on employer name in the main menu and choose 'Edit Details' then switch to the Pay Options tab.
You'll see that you can set the pay frequency, amount and many other fields.
When you create a new employee these are the settings they'll be given, but you can still edit them on a per employee basis.