"The computer started using the windows installation media"

Solution
Anyway - recovery partition houses files for recovery environment.
Windows install might decide to overwrite it (usually it just creates additional recovery partition if necessary).

I'd suggest you backup your user files to another device before upgrading - USB flash drive would be great for this.


It doesn't let me upgrade. I click upgrade and this message shows up along with other stuff I don't remember
 


Ok so if I do a custom install and choose C: as the main partition, D: (it's a partition called Recovery, never understood its use or why it's there) will be unaffected right? Because I want to save the important files there
 
Anyway - recovery partition houses files for recovery environment.
Windows install might decide to overwrite it (usually it just creates additional recovery partition if necessary).

I'd suggest you backup your user files to another device before upgrading - USB flash drive would be great for this.
 
Solution
Just scroll the disk list up.
It should show something like this:
disk-management-windows-10-58ac6f9c5f9b58a3c92d1c3c.PNG