After five years, ABC News anchor Diane Sawyer is stepping down as the anchor of "World News" later this year to take on a new role conducting in-depth investigations and enterprise reporting.

The network announced on Wednesday that Sawyer will be replaced by David Muir, the program's weekend anchor, starting on Sept. 2. Sawyer has been the anchor of the network's flagship program since late 2009, while Muir has been the weekend anchor since 2011, in addition to the co-anchor of "20/20."

Sawyer will now "concentrate full time on new programming," producing specials and doing interviews, ABC said, according to the Huffington Post.

According to sources, the move was "entirely her decision." She says she'll be "dedicated to enterprise reporting, innovative approaches to breaking news and new ways of thinking about big issues and events around the world," reports USA Today.

In the meantime, Muir is expected to substitute for Sawyer this summer when she takes time off, reports the New York Daily News.

"As much as she loved leading World News to new heights -- with so much important, brilliant and impactful reporting and a number one finish in the May sweep -- Diane decided that now is the moment to concentrate full time on tackling big issues in new ways," ABC News chief James Goldston wrote in a memo obtained by The News.

"For many years to come Diane will be a driving force at ABC News with her exceptional storytelling genius. She will create innovative television specials and events, and, of course, continue to conduct the biggest interviews with the most important and extraordinary people in the world," Goldston wrote.

In addition to Sawyer's new role, popular ABC anchor George Stephanopoulos was named the network's "chief anchor" and will lead ABC's election coverage, starting with the midterm elections in November. However, he will remain as the co-host of "Good Morning America" and the host of ABC's "This Week."

"George will be our lead anchor for major special events and breaking news at ABC, driving our live network coverage for the biggest stories," Goldston wrote.