Why is my PC not upgrading to a higher build of Windows 10?

[Windows Central Question]

I am on build 10240, which I am pretty sure was the initial release back in July of 2015. I have since signed up for insider preview, and have been signed up for it in the fast ring for many months now, yet my build is still 10240. I really want to be able to upgrade to the most recent builds to take advantage of saving apps to SD cards, which in my current build is Grayed out. Any assistance is appreciated. Thank you