The Uptons will join Heyward, who won his first Gold Glove in right field last season, to form one of baseball's best outfields. Justin, who played right field in Arizona, said he agreed to move to left field because Heyward "has the hardware."
"I haven't played left at all," Justin said.
"The more reps I can get from the left side of the field is going to be key in spring training. It should be a pretty smooth transition. Obviously it's a change so it's going to take some time but I think I can get used to it."
Justin, an All-Star in 2009 and 2011, has averaged 23 homers, 78 RBIs and 19 stolen bases the last four seasons. He finished fourth in the MVP voting in 2011 when he hit .289 with 31 homers, 88 RBIs and 21 steals. He hit a career-high .300 in 2009.
"We think he gives us one of the most dynamic outfields in all of baseball," Wren said. "We think it really improves what we've been looking to do over last few years, to get younger and more athletic and have that kind of offense that can be explosive."
The Braves gave up former All-Star infielder Martin Prado, one of their top pitching prospects, Randall Delgado, and three minor leaguers in the deal with Arizona.
Atlanta also will have to adjust to the retirement of third baseman Chipper Jones and the exit of centerfielder and leadoff hitter Michael Bourn, who was not re-signed.
Wren said the 2013 Braves' lineup will be "much improved from a year ago."
Added Justin Upton: "We want to win a World Series and on paper I think we're good enough to do it. We have the players to do it."