This is the information I used to do a clean install from 8.1 to 10.
1.First, download the Surface Pro 3 recovery media from Microsoft
2.Next, extract the contents of the downloaded ZIP file onto a USB drive that has been formatted with the FAT32 filesystem. You will need at least 16GB of on the drive.
3.With your Surface powered off, insert the USB drive.
4.Press and hold the Volume Down button, and then press and release the Power button. When the Surface logo appears, release the Volume Down button.
5.Choose your language and country, and then go to Troubleshoot > Advanced Options > Command Prompt.
6.Type "diskpart" then press Enter
7.Type "select disk system" then press Enter. This action will select the drive that the operating system is loaded on. There's no turning back after this next step…
8.Type "clean" then press Enter. Your hard drive is now erased.
9.Type "exit" then press Enter
10.Turn off your Surface and power it on using the method in Step 4
11.Choose your language and country, and then go to Troubleshoot > Reset your PC
12.Click Next
13.Click "Yes, repartition the drives."
14.Follow the prompts to begin the recovery process
15.If prompted, confirm that you want to clear the TPM (trusted Platform Module) by pressing F12
Your Surface will now boot up and finish the installation. You then will be directed to the initial device setup, starting with Region and Language settings.