Losing weight by walking

I literally want to loose 100 pounds. I’m around 250 and use to weight 145-150. I was just looking at old pics of myself and I was like damnnnnn I looked so good. I used to care what I looked like and applied myself and picked out outfits and did my hair and makeup and now I’m like ehhh whatever I don’t care. But I use to walk all the time. Every day after school I’d walk the whole neighborhood and then when I got back home I’d hope on my parents treadmill and walk more miles. Now I just come home make dinner shower and go to bed. I’m literally the definition of lazy. Has anyone had real success from just walking? How many miles did you walk and how’d you track it? Help me out!!