Acer Aspire ES 14 - Changing between Windows 7 and 8.1 During Startup

36 - Changing your Windows version
Press <Enter>, then use the arrow keys to select UEFI or Legacy
BIOS.
Press <Enter> again.
Finally, press <F10> to save the settings and reboot.
Changing between Windows 7 and 8.1 during
startup
1. Turn on your computer and press <Alt> + <F10> when you see the
Acer logo during boot up to launch Acer Recovery Management.
2. Select Restore Operating System to Factory Defaults.
3. Select which operating system to restore: Windows 7 or Windows
8.1.
4. Click OK and follow the instructions to complete the process and
recover your system to it’s factory-loaded condition.
Note
This process may take a few minutes; please plug in your computer’s power
adapter.