I agree, that sounds like a lot over a short period of time. Unless you are also checking in with a doctor or something to make sure you do so safely.
One thing to watch out for is dehydration. A lot of "loose weight quick" schemes involve loosing a lot of water weight. Obviously, this is not exactly a good thing.
Another thing to keep in mind is the longevity of the weight loss. A lot of times, quick weight loss can be effective but then people stop once hitting that goal, stop the new habits, and the weight not only rebounds but then gets harder to remove a second time. The body likes holding onto fat as an emergency measure. Loosing weight slowly can be a bit more manageable since you can start with small changes that you can more easily adjust to.
As for the how, well, unfortunately at the end of the day you'll never be able to outrun your fork. It's gonna boil down to calories in, calories out. (Well, mostly. There are medications, health problems, and other factors at play too. But for the discussion, we're gonna overlysimplify a little here.) There are tons of diets out there, all with different pros and cons (and the amount of each can definitely vary). I use to count my calories, but that was stressful so I'm trying to adjust my diet to have more low calorie items as well as improving mindfulness while eating and impulse control with snacking. But it's a journey no matter what option you choose.
There's also some medications out there or procedures that can help depending on your weight and the weight loss goal. But keep in mind that there's no miracle drug or procedure. They all have some risk or drawback so you'll have to keep that in mind to figure out the best route to take.