Is it OK to delete older versions of Windows 10 SDK?

I just installed the latest SDK(10.0.10586.0) and was wondering if I can delete the libraries from the older Windows 10 SDKs(10.0.10240.0 and 10.0.10150.0)?

Or is there a safe way or a program to do this?

You can uninstall the older versions via Add/Remove Programs. It maintains a different entry for each version.

If storage space is a pressing issue for you, you can proceed to delete the older SDKs. Deletion can be done via program files in pre Windows 10 Creators Update builds or from Settings in newer Windows 10 builds. However an ideal software should provide a good backward compatibility at least within a major version of Windows which at this point is Windows 10.

Imagine someone with an early build of Windows 10 being unable to download your app from the store. You lose users/customers just because they have to update their OS all the way which many avoid altogether.

Keeping the older SDKs will allow you choose a minimum Windows 10 build that your app should support and hence allow installation from devices on those builds.