Here you can learn about how to unpost the voucher.
Login in with Fresa Gold, Navigate to Accounts->All Vouchers, select any voucher status as Posted(Fig.1)
2. Now click Change Status button select the New Status as Unpost and enter the remarks and click Save button(Fig.2).
3. Now the voucher Status is unposted Successfully (Fig.3)
Once you unpost the voucher you cannot change the voucher status as Created.
Hope you got an idea about how to unpost the voucher.