Acer TravelMate P255-MP - Manual (Page 34)

34 - Changing to Windows 8.1 or Windows 7
3. Select Windows 8.1, and then click OK and follow the instructions.
Windows will restart, replace Windows 7 with Windows 8.1, and then
start the Windows 8.1 setup process.
Changing to Windows 7
Note
After configuring Windows 8.1, enter the BIOS (press when starting
your computer) enter the Boot menu and change the Boot Mode to UEFI.
See Changing BIOS settings on page 35 .
Note
To change back to Windows 7, you must change Boot Mode back to Legacy
BIOS. Windows 7 will not start if the BIOS Mode is set to UEFI.
See Changing BIOS settings on page 35