Twitter is changing to address a paradox about a service that revolves around messages limited to just 140 characters. As simple as it sounds, the concept remains too confusing and frustrating for a lot of people.

A redesign is supposed to make Twitter easier to navigate. It offers more accessible features that customize the experience for each user. The service is also expanding users’ profile pages to accommodate more detailed information about brands in text, photos and video as Twitter tries to convert more companies into advertisers.

Twitter’s tweaks debuted in a Thursday update to its software for smartphones and tablet computers. The new look will be gradually rolled out on its website during the next few weeks.

The service will feature tabs at the top of the screen that let users more easily access their home pages, connect with others and discover new content. (Red Twitter’s blog about the changes here.)

“As other services tack feature after feature after feature on top of each other, we’re going to go in an entirely different direction and offer simplicity in a world of complexity,” Chief Executive Officer Dick Costolo said. “This new Twitter is really a foundation for us.”

Twitter is enhancing the service to win over more users and make the site more attractive to advertisers. The company has been coping with executive turnover and a slow rollout of its ad program, which promises to be its main source of revenue.

Co-founders Evan Williams and Biz Stone have lessened their involvement under Costolo, who took the reins in October 2010. Mike Abbott, a vice president in charge of engineering, also has stepped down.

Stone and Williams are concentrating on a startup incubator called Obvious Corp., leaving Twitter without the full attention of any of its creators. Co-founder Jack Dorsey divides his time between Twitter and mobile-payment company Square Inc.

As part of the upgrades, Twitter’s Timeline feature will be 500 percent faster than three or four months ago. The Timeline provides a scrolling list of messages, putting the most recent posts at the top. Users’ profile sections also will redesigned.

Twitter now has more than 100 million active users who post an average of 250 million messages, or “tweets,” a day. The company says the growth in new accounts has increased by 25 percent since October, when Twitter became a feature in the operating system that runs Apple Inc.’s latest iPhones and iPads.

Even so, Twitter executives concluded they needed to make the service even simpler to use and understand to reach its long-term goal of exceeding 1 billion active users.

Twitter will generate $139.5 million this year from ads, according to EMarketer Inc. The research firm pared its estimate from $150 million in September because Twitter has been slow to roll out some services.

Twitter, based in San Francisco, will see ads surge in coming years, especially as it attracts more international advertisers, EMarketer said. Twitter may bring in $259.9 million in ad revenue in 2012, up 86 percent from 2011, the firm estimates. International ad sales will make up 10 percent of the total in 2012, up from 4 percent this year.

(The AP and Bloomberg contributed to this report.)

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