never heard of dell 6530

https://i.dell.com/sites/csdocuments/Shared-Content_data-Sheets_Documents/en/us/optiplex-790-tech-guide.pdf

I think you mean 6350

specifically 1CX3M

https://www.amazon.com/Radeon-HD6350-Profile-Graphic-01CX3M/dp/B01JSP5G1A

I would however recommend a 2 gig 5450 instead of a 512 meg 6350

https://www.amazon.com/VisionTek-Radeon-5450-DVI-I-Graphics/dp/B01CN1F1ZM

You will also need low profile bracket for the 2 gig 5450

https://www.amazon.com/Adecco-LLC-Profile-Bracket-Graphics/dp/B01EW98Z7Y/

DELL OEM

Thank you for your answer. It would be used for full HD youtube / movie for my parents.

"never heard of dell 6530"

here it is: https://www.techpowerup.com/gpu-specs/dell-hd-6350.b743