Welcome to the forum

Good page to bookmark here: Ford Ranger Fluids & Capacities

Manual or automatic transmission use different amounts, but about 15 quarts if empty

It is very hard to get all the old coolant out.
Best method is to drain coolant, then refill with distilled water, and run it that way for 2 days or so, then drain it again and refill with 50/50 mix

And always REVERSE heater hoses at the firewall when you change coolant, do this when you drain old coolant the first time, and turn heat ON in the cab when driving, fan can be off
Water pump will then push out any blockages that can be pushed out of the heater core, and they will be drained out when you drain the distilled water out.