Nick Grimshaw will step down from hosting the BBC Radio 1 breakfast show in September and be replaced by Greg James.

The DJ told listeners he was “really tired” and ready to hand over the early morning slot after doing it for longer than he had expected. This week he became the second-longest serving breakfast show presenter in the station’s history.

“Come September, it will be six years … I’ve decided it’s time for a change, time for a new show and, most importantly, it’s going to be time for a new wake-up time … preferably about 11.30am,” he said.

Grimshaw will remain on Radio 1 and swap jobs with James, who presents the 4-7pm drivetime programme.

James then appeared on the programme and said he felt nervous about announcing his new role as host. “I did not sleep one hour last night just thinking about it … it’s too much,” he told Grimshaw. James added that the hosting job would be a “big challenge” and he was “ready to give this a go”.

Both presenters will work four days a week, as part of a plan to reinvent Radio 1’s schedule by running weekend programming from Friday to Sunday.

Grimshaw was appointed in 2012 to replace the long-serving breakfast show host Chris Moyles, with a mission to reduce the average age of Radio 1’s audience amid fears the station was losing its relevance to young listeners.

He inherited a programme with 7 million listeners a week but during his time in control of the programme, which coincided with the explosive growth of smartphones and social media, this at one point dipped to about 5 million.

Radio 1 bosses point to the industry-wide decline in the overall number of radio listeners aged 15-24, instead highlighting the growth in the station’s following on Facebook and YouTube as evidence they are still relevant to younger audiences.

James, who has been a Radio 1 presenter since 2007, was first considered as a potential candidate for the breakfast show job when Moyles stepped down. Since then the 32-year-old has substantially increased his profile, hosting the primetime BBC One music show Sounds Like Friday Night, writing a series of children’s books, and producing many successful viral videos.

This year the presenter told the Guardian that, unlike Grimshaw, he was “phobic of the celebrity world”.

He also said the station had struggled with its identity in recent years, as part of the attempt to attract younger listeners at all costs, suggesting this had now changed: “Radio 1 appreciates that if you get the mums and dads, then you have people like my niece and nephew who are eight years old, and I think it can start again like that.”

James also co-presents the . This year he attempted to climb Mount Snowdon, Scafell Pike and Ben Nevis in the space of five days while cycling between each one, only to be be forced to call off the attempt due to extreme weather. He eventually resumed the challenge and raised more than £1m for Sport Relief.