A new operating system for Apple's mobile devices is set to come out later this year. iOS 9 will likely be previewed at Apple's Worldwide Developers Conference starting Monday, USA Today reports. 

The new operating system is expected to run more smoothly than preview iOS releases, and it will work on older phones too.

"A lot of people don't want to upgrade, because they don't think the new version will be stable," said Mark Gurman, a senior editor with 9to5Mac, a website that follows everything-Apple. "That will change this year."

The iOS 8 release debuted last fall and it caused many users to complain about battery and WiFi issues with the new software.

Many users will at first avoid updating to the latest iOS but will eventually do so, Peter Csathy, CEO of the Los Angeles-based venture capital firm Manatt Digital Media, said.

"At the end of the day, they like getting the new features," Csathy said. 

Some of the new features expected to make it into iOS 9, according to 9to5Mac are below.

iOS 9 will work faster, but it will not require a huge amount of space. iOS 8 required at least 2 GB of free storage space to be installed onto phones. Users with limited amount of storage space on their iPhones had to find a way to clear up at least 2 GB. Apple has now reportedly found a way to get iOS 9 onto phones in a much smaller size. 

"This will be a big improvement on older devices," Gurman said. 

Notifications will improve. Apple's Calendar, Contacts and Passbook apps will work together to provide better notifications. The notifications will alert users with updates on their day and their interests.

There is a new keyboard planned for iOS 9. This new keyboard will also allow for a new font. Android's operating system allows for different fonts and Apple could be taking a page from their book.

Security is expected to increase in the new operating system. Tim Bajarin says that Apple wants to be an industry leader in security.

"Apple's goal is to make all of their devices the most secure on the market," he said. 

Users were slow to upgrade to iOS 8, fearing that the new software would make their phone run slower or cause it to malfunction once they upgraded.

CNet explains that Siri should also be improved in iOS 9. More automatic notifications are expected and the search functionality should improve as well.