I know literally nothing about PCs and want to upgrade my storage

Hi!
First time posting and hoping yall can help!
I know literally nothing about pcs and specs (I originally bought a pre made one)

I currently have a 500gb WD SN570 (along with a 2tb external hard drive) and I’m wanting to add more internal storage for gaming.

I have no idea how to add or what I can add and I just need somebody to explain it to me in layman’s terms because google is confusing the fuck out of me 😂😭

I’ve attached my specs and the motherboard manual page (I’ll put in comments cause it’s not letting me attach the image 🫡)
Please help and thank you ✨