Twitter CEO Jack Dorsey announced Sunday that four department heads would be leaving their positions. This is the biggest move Dorsey has made since he returned to the company in mid-2015.

Dorsey announced the news of the dismissals in a tweet.

Leaving on Good Terms

Dorsey wanted to make it clear in his note the employees are choosing to leave, not being forced to leave, and they are leaving on good terms.

Leaving the company are head of media Katie Jacobs Stanton, product chief Kevin Weil, engineering chief Alex Roetter and human resources leader Brian "Skip" Schipper.

The former executives were mostly happy with their time at Twitter. Stanton said he wanted to focus more time on his family, and Roetter said he had been thinking of leaving the company for "a while."

Twitanic: Saving a Sinking Company

Dorsey is trying to reverse the company's recent failures by shaking up the staff. Since Dorsey took over as the CEO in 2015, Twitter's stock has fallen nearly 50 percent, CNet reports.

Twitter is trying to find its identity while trying to stay competitive with Facebook and Instagram. Facebook has over 1.2 billion monthly users, and the photo-sharing service Instagram has over 400 million. Twitter still is struggling with 316 million users (as of July 2015) and has been around four years longer than Instagram.

New Features Coming?

Twitter users have been hesitant to accepting some of the changes that have been added to the service. The most recent change traded the "favorite" button to a "like" button. The new "Moments" feature tries to make a "best of Twitter" topic list based on trending news and events. In the future, tweets could be as long as 10,000 characters instead of the current 140 character limit.

Twitter knows they need to keep the product fresh to attract new users, but they have to be careful not to anger their current users with multiple unpopular changes.