Acer W510 tablet comes with Windows 8 Home and Premium pre-installed. You can upgrade this version to Windows 8.1 for free via Windows App Store. However, if you want to install clean version of Windows 8.1, there are couple of tricks you need to know.  

• Disable secure boot in Acer W510 BIOS
• Boot from Windows 8.1 bootable USB or external DVD drive
• When Windows 8.1 setup prompts to provide license / serial key, instead of using your real Windows 8 key, enter following generic Windows 8.1 license number: XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB.
• Once Windows is installed, go to Control Panel > System > Change Product Key and enter your real Windows 8 license key.

The main trick here is to use generic Windows 8.1 license key during installation. Even though Windows 8.1 upgrade is free to all Windows 8.0 users, for some reason (better known to Microsoft) Windows 8.0 license keys don’t work during clean Windows 8.1 installation. But you can activate Windows 8.1 using 8.0 license key after installation.