Acer TravelMate P645-V - Manual (Page 49)

Changing to Windows 8 or Windows 7 37
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Note: After configuring Windows 8, enter the BIOS (press when
starting your computer) enter the Boot menu and change the Boot Mode
to UEFI.
Please refer to "Changing BIOS settings" on page 38.
Changing to Windows 7
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.
Please refer to "Changing BIOS settings" on page 38.
Start Windows 8; from Start, type ‘recovery’ to open Acer Recovery
Management.
1. Select Restore Factory Settings.
2. Select Yes.
3. Windows 7, and then click OK and follow the instructions.
Windows will restart, replace Windows 8 with Windows 7, and then start the
Windows 7 setup process.