It's a pain as you have to delete 1 ride at a time.
1. Press bottom left button (history).
2. Use bottom right button to scroll down to "all rides".
3. Press bottom left button to select.
4. Press bottom left again to select whatever ride you want to delete (you can scroll through them with the right hand buttons).
5. Once a ride is selected, press bottom left (options) then scroll down with bottom right to "delete ride".
6. Press bottom left to "select". It will then ask you if you're sure you want to delete! Bottom right for "yes".
It will then take you back to step 4 where you can select another ride and repeat steps 5 and 6.
Once you find your rhythm it's quite easy as you just press bottom left twice, bottom right twice, bottom left once, bottom right once. And repeat.....