If driving the easiest way is to drive down Currie Street and park in the spaces down from the Carpet Warehouse.  Then cross over and walk up the short, steep road called Church Square.   

Alternatively, if you’re familiar with Duns simply park in the Market Square and walk through the alleyway between the Post Office and Fantoosh (next to George Romanes Chemist).  You’ll see the church in front of you and if you bear left, the main door is just round the corner from the church noticeboard.