The simplest way is to gross up the ordinary annuity (payments in arrears) by a single period at the discounting rate.
For example, if the ordinary annuity has semi-annual payments (half yearly) and the PV is $1000 using a discounting rate of 5% p.a., then the PV of the annuity due would be:
PVDue= $1,000 x ( 1 + 5%/2 ) = $1,025