It is simple, Yaar if u booked the expenses during the year and maintained the accounts through computer, then just modify the entry by debiting to correct account head .
Never do the habit of modifying the voucher, its always suggested to pass a rectification journal.
This is best practise, any body will do mistake but do the rectification entry. This is how you can do it in any Accounting Package unless otherwise you have the Super User Rights and also in the ERP environment .