Don't worry, this is easier than you think!
The AC capacity is the size of your inverter, in Watts. You can simply inspect your solar inverter, to determine the wattage. If you have more than one inverter, add up the total wattage from all inverters to determine your AC capacity. Most inverters report capacity in kilowatts (kW), so be sure to convert to watts by multiplying by 1000.
The DC capacity is the total wattage of all of your solar panels. You'll need to figure out what the 'rating' of your solar panels is, and then sum up the total of all the solar panels in your solar array. The value should be provided in Watts.
If you don't know or can't easily find out these values by inspecting your PV system, you should consult the paperwork from your installation or contact your solar installer to figure them out.