Originally Posted by
manus31 So your saying go back to 8.1.
Then what.Do I need to use windows insider app.Does that still work ?
I Only have option for fast and slow currently on the insider fast build
WDRT only has 8.1 available for the 640 unfortunately. You WILL have to go back before you can continue. You cannot go backwards without using the WDRT. (which is why you only have Fast and Slow options at this time.)
AFTER you're back on Windows Phone 8.1, you can use Windows Insider - Release Preview to get 10.
OR, you can use the Upgrade Advisor to get 10. (do note it'll take two or more updates before you're fully up-to-date.)