I haven't updated my MacBook Pro in many years. In fact, I'm still on Snow Leopard (MacOS X 10.6.8). This is a version so old that all the steps I read to make a bootable USB drive failed. I wasn't able to use createinstallmedia to make a boot disk because that doesn't work until MacOS X 10.7. Nearly all the steps I read online regarding using "Disk Utility" to make a bootable USB drive failed until did the following steps:

1. link.

2. After downloading, it will automatically launch the upgrade installer. Quit with Command+Q.

3. Go to "Applications/Install OS X El Capitan" and Control+Click to...