I want to upgrade my iMac (mid 2011) from Lion to El Capitan. Since this is the first time I have ever upgraded with OS-X, I downloaded Apple's instructions for how to do it. To initiate the installation the instructions say: "To continue, you must enter your username and password." Later it says: "the Mac will restart and you'll need to log in with your username and password." My question is that I don't know what they mean by "username". I know the system password I use when making OS-X changes and I also know my Apple ID email address and password. I use these often. But in the 4.5 years I've had this Mac I don't recall entering a "username". I am the only user and the admin, so did not set it up with multiple accounts. That is, when I turn it on I do not need to "log in". I see no record of writing anything down for a user name when I set up the iMac initially, and I'm pretty careful about doing things like that. My fear is that I will get to this point in the install and not be able to continue and then be locked out of my computer entirely. Is there any way I can determine what the "username" is if it exists? Any other tips or ideas? Thanks!