That's the tip of the iceberg. It won't feel like your own computer until you've been through the whole out-of-box experience - just back it up with Time Machine then wipe it and cleanly reinstall El Capitan. Then go through the whole thing again next week with Sierra.
If there's any application software on there (Office, Adobe CC, or whatever) then it's not licensed to you anyway, so you can't legally keep it.