You can change the terms of your loan up to five times. Each time, you can change the interest rate, the regular repayment, make a one-off payment, or any combination of these. Enter values in the fields you want to change or leave the others blank.
For example, to change your repayment to $250 and make a one-off payment of $5000 at the end of the second payment of your loan, enter a row with "2" for Payment #, "250" for Regular Repayment and "5000" for One-Off Payment.
I've tried to make this calculation match what a bank would actually do, but I can't guarantee it. Whatever you do, check with a bank as well!