We would suggest restructuring the loan if you want to extend it. That way there will be a record also. To do this, please click on the specific loan.You can do this by visiting Borrowers (left menu) >> View Borrowers >> Loans >> View. Or by clicking Loans (left menu) >> View All Loans >> View.
Then, go to the Loan Terms tab. There you will see Restructure Loan button. Once you click this and create a new loan, the old loan will be shown as restructured.
If you want to extend it again, then you can restructure the new loan and keep doing the above.