Help deciding to install storage

[Soulrunner]

So I bought a prebuilt not too long ago and its a little short memory wise. I only have a 500gb ssd. I was thinking I could use this old desktop pc's hdd and put it into my computer. What scares me is I have no idea what is on it and I don't know if it'll mess up my computer. Is there a way to wipe the hard drive without messing up my computer? (edit: I put this post in the wrong place and don't know how to delete it. My bad)

[IHFyrz2812]

is there any os that are in the hdd? , if there was, make sure to prioritize the ssd before you boot, then format the hdd