I have had 500gb HD this whole time but my system has only been showing 250gb on my Windows 10
Solution 1:
Using disk management to reclaim the hard drive does not erase your information. Instead, it allows you to specify the size of the unallocated space that you want to add to the C drive without having any of your data lost.
To do this, select the drive you want to extend; as an example, I clicked C.
Enter the size of the unallocated space you want to add; when you have put the required number you want, click Next, then Finish.