As a windows insider you are now 4 builds above the "full windows 10 ". It would help solve your problem if you could tell us if you meant to be in the insider program.

You are now 4 insider preview builds beyond the RTM build Version 10.0.10240.

If you are in the insider program, you will need to leave the insider program to go back to the RTM build. It cam be found in Settings>Update & Security>Windows Update>Advanced Options. Click the...

Windows released version (RTM) is build 10240. In order to get an insider build you would normally had to click on the "get started" button and follow the directions. Did you want to be in the...

I don't understand what you mean by downgrade. 10565 is the latest insider build. Do you want to get to the non insider (RTM) build?
If you had upgraded from 8.1 to windows 10 and then joined the...