coolant for my car

I have a 04' Ford Crown Victoria P71, I just bought it used and I wanna do some maintenance on it and the coolant level is below the COLD FILL RANGE, so I'd like to know how to do it, should I add more coolant to it, meaning mixing the old and new coolant, will it be fine, or should I best drain it all then add the new coolant to it?
See, I don't even know what type of coolant is in the car, so is it dangerous to mix different types of coolant? The car manual tells me I need 50/50 coolant and distilled water, and tells me to add Motorcraft Premium Gold(yellow-colored), VC-7–A (U.S., except CA and OR), VC-7–B(CA and OR only), meeting Ford Specification
WSS-M97B51–A1.

Help, I'm lost here.

If you're just replacing a little bit (under a gallon) just use water. You won't throw off the mix by more than a couple percent and it won't hurt a thing. If it gets low in the future you can replace it with more yellow coolant. Depending on where you live, concentrations from 70/30 up to 30/70 are acceptable. More anti-freeze will transfer less heat, but prevent corrosion and freezing better. More water will be more efficient at transferring heat, but will freeze at higher temps and possibly allow more corrosion.

I'm in the southern US and I typically do 70/30 or 60/40 (more water than anti-freeze) since it so rarely gets below freezing. When I lived in Canada and Pennsylvania I did 50/50.