The lines you are most likely to want to modify are:
int maPeriodFast=20; //you probably want to set this to 5
int maPeriodSlow=180; //you probably want to set this to 10
Resolution resolution = Resolution.Daily; //you will likely want to change Daily to Minute
SetStartDate(2012, 1, 1); //this should be a reasonable date for minutes, sometime in 2016 most likely if you don't want to wait too long for your backtest
string tickersString =..... //I've got the whole s&p 500 in here. You probably didn't get lucky. You might want to just trade the stocks you've been trading, they might behave appropriately where EMA crosses are concerned.
where stockData.EMAFast>stockData.EMASlow //this one is further down in the Buy routine and indicates that one should buy when the EMAFast is greater than the EMASlow, you can reverse that.
if (stockData.EMAFast < stockData.EMASlow) //this one is further down in the Sell routine. It indicates that one should sell when the EMAFast is less than the EMASlow. You can reverse that.