The Lakers' third-leading scorer was an unheralded off-season signing but outperformed Young through three games.
Henry is averaging 13 points and shooting 40%. Young is averaging 8.3 points and shooting an abysmal 27%.
"Just [trying] to find a better spot for Nick, maybe get a little bit more production out of him," D'Antoni said. "[Henry] has played as well if not better than anybody. There's no reason not to go ahead and do this and lengthen his time on the court a little bit."
Henry, 22, started 18 games in his first three NBA seasons. He accepted his promotion without any fanfare.
"I'm not too amped up or doing anything crazy," Henry said. "I'm going to do the exact same thing I've been doing."
Henry was a relative unknown when he joined the team as a training-camp invitee. He was the 12th pick in the 2010 draft but averaged only 4.5 points in 133 games with Memphis and New Orleans.
He has always been a hard-charging slasher to the basket but added some outside touch while working with Lakers assistant coach Kurt Rambis.
Henry received nine stitches in his forehead Friday night when he smashed into Wesley Johnson's knee on a drive to the basket against San Antonio. He acknowledged he still had some headaches.
"It's getting better every day," Henry said. "It'll be probably gone within the next couple days but I'm fine."