Hi toopearthmoving,
I'll be happy to answer this for you.
When you go into the Employees tab, go into the pay run and select the employee you wish to adjust the PAYG for.
Select the green Actions button then select Adjust PAYG.
From here you are able to either add or substract value depending on how you need to adjust the PAYG for the employee!
Once you're finished you can select Save.
I hope this clears things up for you, let me know if it doesn't and I can give you some further support.
Kristian.