Hi,
To change the Ads listing currency, open your joomla admin and click components-->Jomclassifieds-->General Configuration-- Layout Settings. Here add your currency (MYR) in the Multi-currency field and then select this currency (MYR) in the Default Currency field. Finally save it and check your Front-end.
To change the Payment currency, open your joomla admin and click components-->Jomclassifieds-->General Configuration--Payments Options. Here change the currency from USD to MYR. Finally save it and check your front-end.
Thanks.