Imac Reinstallment

Hi

I have IMAC mid 2011 that was a gift from my aunt. My aunt couldn’t remember her apple ID. I wanted to delete all the file or simply reinstalled it. I followed the step sunc as pressing the power button at the same time the command plus R, etc. I tried also reinstalling it to the USB stick with 16 gb. But in the end The system says ‘Can’t download the additional components needed to install Mac OS X.

I went to the apple shop but they advice me to downgrade the Imac since it is too old. So i can’t use the computer properly. I mean I can only open the MAX OS X Utilities.

Can someone help me on this?

I really appreciate if you can.

Thank you.