Windows 10: How to delete old OS partitions from HDD. Using cleaned installed new OS from a m.2?

How to delete old HDD OS. Used to have my windows on a HDD and Cleaned Installed on a new M.2. I'm ok with losing the files of the old HDD windows but I partitioned drive that has 500mb of storage that I cant delete.I have a new MoBo and Processor that has m.2. I clean installed in the m.2 which means that I don't need windows 10 on my old HDD. That HDD Disk 1 has 1+3 partitions. The partitions are OS H:, Systems Resereved, 519MB HealthRecovery, and the MOVIES I:. I cannot and dont want to reformat the whole drive,Is there a way to just reformat drive H: and the Systems Reserved and He

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Cloned OS to SSD want to delete old OS on hdd

Not sure if this was answered(cant find 1) but recently cloned windows 10 from HDD to SSD. My HDD was setup as GPT and the partition was setup with the OS as almost the full 1tb size. I had and currently have alot of used space that i dont wanna lose if
it can be avoided. The whole cloning process was a pain having to move stuff to the ssd then partition the empty space on hdd the move stuff to the new partition until I had less than 200g with the OS still there so I can clone it onto ssd after cleaning
it. Os works fine(windows loads sooo much faster) old hdd works fine but wanna get rid of the old os on hdd without deleting anything else? Sorry so long and sadly I merged the partitions back to 1.

 

Installing 2 OSes in the same HDD

How do you install another OS on the same HDD? Do I just create another Partition and install the new OS in it? If so, how do I switch between the 2 OSes?

 

Remove an OS installation without removing files?

There's no way to keep files and delete OS without installing a new OS. You can create a new partition on that drive, drop your files there and format partition with OS.