Question about OS migration

I just need some help with how to go about getting my computer, specifically Steam, to run through my OS I copied onto a new SSD I got to help improve performance on games. I used DiskGenius to migrate the OS over to the SSD, but now looking at my disk manager the OS is just present on both the new SSD and old HDD. How should I go about getting rid of this old copy so that everything goes through the SSD, and in doing so do I run the risk of bricking my whole computer or anything like that?