I tried to upgrade from Snow Leopard to El Capitan but I got an error message saying it couldn't be installed. What other options do I have?
What is the message? Since you have not told us what year or model Mac you have, we have no way of knowing what you can upgrade your OS to. I suggest you click on the link below and read the information there and then reposting.
Writing an Effective Apple Support Communities Question - Apple Community
Maybe my tip here, might help you isolate what step you missed:
I tried to upgrade from Snow Leopard to El Capitan but I got an error message saying it couldn't be installed. What other options do I have?
