Jo Whiley is to be dropped from her prime Radio 1 morning slot after eight years, with Fearne Cotton taking over.
The 44-year-old presenter, who hosts the 10am mid-morning show, will leave in September and take up a new weekend programme.
Also leaving her weekday show is Edith Bowman, who vacates her 1pm show and heads to the weekend breakfast programme. She will be replaced by early morning presenter Greg James.
Jo had previously hosted a lunchtime show for Radio 1, as well as the Evening Session with Steve Lamacq.
She said on Thursday: "After eight wonderful years the time has come to move on and give someone else the privilege of entertaining the nation on a daily basis. I've had the most amazing time ever.
"The prospect of lie-ins, taking my kids to school and doing something new is, I confess, rather exciting. I will, of course, be taking the keys to the Live Lounge (her live music spot) with me to my new weekend show - so the live music will continue - but I'll be leaving behind a spare set for Fearne."
Fearne said of her role: "I love being at Radio 1 and taking on a weekday show is a dream come true.
"Jo is leaving very big shoes for me to fill and it's nerve-wracking. She has been a massive inspiration to me throughout my career so I have a high standard to live up to."
Fearne already co-hosts weekend shows with Reggie Yates, which he will now continue to present alone. Other changes include weekend breakfast host Dev moving to the early breakfast show vacated by Greg James.
The changes kick in on September 21.