SAN FRANCISCO — Apple plans an overhaul of iTunes that would mark one of the largest changes to the world’s biggest music store since its 2003 debut, people with direct knowledge of the matter said.

Apple will unveil the changes by year’s end, said the people, who asked not to be identified. Apple will more closely integrate its iCloud file-storage service with iTunes so users can more seamlessly access and manage music, videos, and downloaded apps across different Apple gadgets. Apple also plans new features for sharing music, the people said.

ITunes has been critical to Apple’s success, generating revenue of almost $1.9 billion last quarter alone.

Apple declined to comment.

Apple’s iTunes Store has more than 28 million songs and 45,000 movies. It also houses the App Store, which offers more than 650,000 applications.

With an increasing amount of content available on the store, the overhaul is intended to improve how people manage all their files, one person said.

One of the main ways Apple will attempt to improve discovery is by making it easier for people to share songs, a popular feature of Spotify ‘s music-subscription service.