If you're preparing to migrate to Windows 10, the first thing you might possibly run into trouble with is actually downloading the OS. It takes a certain amount of free space on your drive to install a new operating system so that it can be updated and certain components can be effectively managed.
The storage requirement for Windows 10 is 16GB, which should be held free of charge on the main system drive that the device makes. Currently, this is the same as earlier versions of Windows, but you can most possibly do it again if you've updated before.
If you'd like to check how much storage is left on your device, go to My Computer (or This Computer, based on the version of Windows you are going to run), where any drives you have will be identified. The remaining space below each drive can be seen, or you can right-click and choose Properties for a clear view.