How to downgrade from windows 10 technical preview back to windows 8.1?

I have resolved this issue by contacting Microsoft surface pro support and  got instructions by email 📧.

Support person was great and responsible....!!!

Using 16 GB USB flash drive was able to go back to Windows 8.1 in my surface pro 2. Took less than an hour.

Though I didn't take recovery image backup, was able to download from MS site. Great

Email if someone has the same

issue

We have here the steps we need to do to change your WIndows 10 back to Windows 8.1
 
This link will allow you to download the Recovery image:
 
http://www.microsoft.com/surface/en-ca/support/storage-files-and-folders/create-a-recovery-drive
 
Please make sure that you are logged in to your Microsoft account so that you can download the image.  You need to choose the Surface Pro 2 form the list.
 
The data we need would be 16GB.  It is a good practice that we use a flash drive that is atleast 32GB to make sure that the image will be saved properly.  After downloading the image, please follow the instructions to use it on this link:
 
http://www.microsoft.com/surface/en-ca/support/warranty-service-and-recovery/usbrecovery
 
The next thing to do will be to follow the steps below:
 
Make sure that Surface is shut down and plugged in. 
Insert the USB recovery drive into the USB port on Surface. 
Press and hold the volume-down button while you press and release the power button on your Surface. 
When the Surface logo appears, release the volume-down button. 
When prompted, select the language and keyboard layout you want. 
Tap or click Troubleshoot, then tap or click Advanced Options, and then tap or click Command Prompt. 
At the command prompt, type diskpart.exe and press Enter. 
Type LIST DISK and press Enter.
Type SELECT DISK SYSTEM and press Enter. 
Type CLEAN and press Enter. 
Type EXIT and press Enter. 
Close the Command Prompt by clicking the "X" in the upper right corner.
Tap or click Troubleshoot, and then tap or click Reset your PC. 
On the Reset your PC screen, choose Next. 
If prompted for a recovery key, tap or click Skip this drive at the bottom of the screen. O 
Tap or click Yes, repartition the drives, and on the next page, tap or click Next. 
Choose either Just remove my files or Fully clean the drive. The option to clean the drive is more secure, but takes much longer. For example, if you are recycling your Surface, you should choose to clean the drive. If you are keeping your Surface, you just need to remove your files. 
Tap or click Reset. 
 Surface will restart and the Surface logo displays while the reset process completes (this can take several minutes).  
During recovery, at American Megatrends screen, press Esc. 
If the customer is shown the UEFI screen, press Save & Exit.
Once the steps are done, your Surface Pro 2 should now be back to Windows 8.1
 
If you have any questions or clarifications, please reply to this email.  I will keep your case open until you are successful in reverting back to Windows 8.1.

I installed windows 10 technical preview on my laptop, i want to go back to 8.1 but dont know how? i tried recovery but it just recovered the windows 10 preview! :/

The fine print, before installation was that you will not be able to go back to windows 8.1 without a usb / dvd recovery disk. They repeated it several times stating we shoudl make sure to have that if we ever want to go back to previous window because we will NOT be able to go back.

My suggestion would be is to locate your usb/recovery disk...if you do not have one, order it from your pc manufacturer