Can't upgrade 2011 MBP from Snow Leopard

I have an old (early 2011) 13 inch MBP. It has a spinner platter drive, but I did upgrade it too 8 GB of RAM a while back. I want to give it to a family member to use, so when I went to use the disk utility to erase the drive, I realized you can't do that on snow leopard, and the update utility only gives me the latest build of snow leopard.

I figured out I have to download El Capitan from Apple and install that before upgrading any further/wiping the disk. So I downloaded it, installed it, it said "install successful" after about 15 mins, and then....nothing. The machine didn't restart, nothing changed, and when I rebooted it was still running Snow Leopard. What the hell? I'm out of ideas and my family member is leaving soon to drive back to their home state. Any ideas?