Chowk Yadgar is the central square of the Old Peshawar; this is a good place to get orientated again after walking around in the small streets. The monument in the middle of the square remembers the heroes of the war between India and Pakistan (1965) and is the reunion place for the old men.
On the West Side of Chowk Yadgar you can see the moneychangers, you can see them sitting on their small carpets, a big safe behind them and armed with a mini calculator. They can change all kind of money, however it is illegal, so I believe it is better to go to a bank for changing.