As per the reddit post from "btchip":
"Yes, you can update to MCU 1.1 by connecting the device to Ledger Manager while in bootloader mode (boot while holding the left button) - that's not necessary if your device isn't strangely freezing from time to time though"

In any case, I just tried this and it worked fine.

- Open up the Ledger Manager
- Hold down the "left" button on the Ledger Nano S (on my this is the one nearest the usb port)
- While still holding down the left button, connect the Ledger Nano S to the computer
- Keep holding the button

The Ledger Nano S should start up (you'll see the Ledger logo, then it should say "Bootloader" and the MCU will autoupdate