The easiest way is to write another cheque, and write a big word "VOID" on the wrong one.
If you want to correct a cheque, write a line across your mistake and write the correction above it. You should sign next to your correction to authenticate it.
If the mistake is made on the payee name or on the date, it may be possible to correct it and the cheque is still acceptable. However, bank must not accept correction made on amount. Please note that bank may not accept a corrected cheque. You should consult your bank and check if it is acceptable by the bank.