Kelly Osbourne is set to join Radio 1, and Chris Moyles' breakfast show will get an extra 30 minutes, in a shake-up of the station's schedule.
Osbourne will present Radio1's Surgery on Sunday evenings
Osbourne, who joins the West End cast of Chicago next week, will host Radio 1's Surgery - part of the new "teen zone" on Sunday evenings.
The Chris Moyles Show will now start at 0630, while chart hosts JK and Joel are leaving the station after three years.
The schedule changes will come into effect on 12 October.
The Chris Moyles Show, which has 7.26 million listeners, will start 30 minutes earlier from 15 October.
Moyles, whose listener numbers are catching up with the UK's most popular breakfast DJ Terry Wogan on Radio 2, said: "I'm really pleased with my extension.
"We always run out of time on the show so it'll be great having an extra half hour a day. Although because it means getting up earlier I'll probably be late more often!"
As a result of the revamp, current hosts of the Radio 1's Chart Show and early breakfast show, JK and Joel, will leave the station after three years.
Newcomer Greg James, 21 - who was plucked fresh from student radio - will take over their early breakfast slot, while Fearne Cotton and Reggie Yates will take over the chart show.
Speaking of their departure JK and Joel said: "We've had a great time at Radio 1... and have presented some of the biggest shows on the network".
Friday evenings will now be dedicated to dance music genres, while urban music becomes the focus of Saturday nights.
Sunday evenings will now become the "teen zone" aimed at under-18s, along with Radio 1's Surgery hosted by Osbourne.
The "teen zone" focuses on issues surrounding young people from relationships to education.
Other changes will see Nihal take over from Cotton and Yates on the weekend breakfast show, while TV duo Dick and Dom are being drafted in for a new Sunday morning show.
The overhaul comes as the station approaches its 40th anniversary.
Radio 1 controller Andy Parfitt said: "It's important that we keep up the pace of change and innovation both on air and online.
"This simplifies and strengthens Radio 1 and is an important step in providing programmes focussed on the under-18 audience."