Hello, Jovial Mobius
Welcome to the Microsoft Support community.
I noticed you want to change your drive setup like change boot drive and allocate your spare hard drive, right?
The easiest way to change the boot drive for every day user would be to use Windows installation media to install a new Windows to new Drive.
This way you can see boot selection menu during boot up to let you choose the different Windows you have on your device.
and reinstall third-party application like game there----- You can reimport them if you have local game file in most of the case.
In your case, since you have one SSD only it is not recommended to move your system to another device as SSD is much faster that HDD in most of the case therefore it is ideal for system drive. Plus, you have a 300GB SSD which should be enough for system drive as long as you download those big game to another drive.
If you do not have many experience the build in drive partitioner for Windows would be ok for you despite do not have many advance features compared to some paid software:
- Go to Control Panel > System and Security > Administrative Tools, and then double-click Computer Management.
- In the left pane, under Storage, select Disk Management.
- Right-click an unallocated region on your hard disk, and then select New Simple Volume.
- Enter the size of the volume you want to create in megabytes (MB), and then select Next.
--- For other option you can pretty much left with default one. If you have any doubt, feel free to ask me in this post.
Looking forward to your reply.
Best Regards
Benjamin - MSFT | Microsoft Support Community Specialist