The hockey-side of that change began last summer following the draft and subsequent prospect camp. Day said the front office liked what they had in him, but that work needed to be done.
"The Rangers management - they were really good to me and just told me to just be myself," Day told NYRangers.com in a phone interview Wednesday. "We know what you can do. You have the skill set that we want but you just have to get your conditioning levels up to par.
"That's what I did this offseason," Day continued. "I got into really good shape. I know they're happy with where I am."
"This is a big accomplishment for any young hockey player, to get drafted and sign an NHL contract," Rangers Assistant General Manager Chris Drury said. "This is the first step in what we hope is a long career as a Ranger."
On the ice, Day - who was acquired by the Windsor Spitfires of the Ontario Hockey League from Mississauga earlier this season - said he's become a more balanced player who is dangerous in both ends of the ice.
"I was always a big guy and I could skate a lot but I never put that together to be a full package," said Day, whose career-high 14 goals ranks sixth among OHL defensemen in 2016-17. "This year, I'm playing offensively and defensively strong. I'm a plus-19 this year where the last couple I've been a minus and I'm putting up points with it. It's been a real fun year so far."
Adam Graves said he's impressed with the way Day has become a "complete" player this season with the Spitfires.
"I think with all young players … consistency is a big part of anyone's success," Graves said. "He has really added that element this year. I think his confidence has grown. I think he's taken this opportunity and he's really focused on his game. You can see the fruits of his labor."
Day, who was granted exceptional status to join the OHL as a 15-year-old, said he's also done a better job managing the mental aspects of the game.
"I just think my mental attitude - I don't take things as hard anymore," Day said. "Management is there to help you with positive criticism. I've sounded out everything and took everything really positively and it's helped out this year."
Spitfires Vice President and General Manager Warren Rychel said he's seen an improvement in Day's defensive play since he coming over from the Steelheads in October.
"He's a little more defensively structured," said Rychel, a former NHLer of 406 games. "Before, he just took off up the ice at will. That's not necessarily the case now. He's been paying attention to his defensive responsibilities a lot more. We're working with him to be more consistent in his own end."
Drury echoed those sentiments. He said while Day has always been known as a great skater, that's only one aspect of his game that he's seen take strides since September's training camp, when the Rangers kept Day around longer than nearly all the prospects who were sent back to junior.
"You can't not watch him and not notice how great of a skater he is, but I think he has a lot other skills besides that," Drury said. "He's a big, strong kid that's really only scratched the surface as far as training. He's got to be one of the strongest players in that League. I think the upside in that department is huge."
While Day did not crack a spot on Team USA's roster for this year's World Junior Championship, Drury said that after talking with people from USA Hockey that he fully expects Day to be a strong contender for a spot for next year's tournament in Buffalo.
"I recently saw some USA Hockey World Junior staff members and they have been hearing the same reports around the hockey world as we have in that he's been making strides and developing into a more well-rounded player and is certainly on their radar for next year's tournament."
