I'd like to finally upgrade, perhaps to Mojave. How can I do this? I've tried to follow some instructions on these forums from 2018 and such, but they don't work. Can anyone suggest safe ways to upgrade my old MacBook Pro (Retina, 13-inch, Early 2013)?
You can download the macOS installers from links contained within this Apple article which also includes instructions for creating a bootable macOS USB installer:
https://support.apple.com/en-us/HT201372
I highly recommend you create a bootable macOS USB installer so you have more options in case something goes wrong. You can just run the installer from within macOS as well, but if you don't have access to another compatible Mac having a USB installer is a good thing to have ready if something goes wrong.
Make sure to have a good backup before attempting to upgrade macOS.
You can download the macOS installers from links contained within this Apple article which also includes instructions for creating a bootable macOS USB installer:
https://support.apple.com/en-us/HT201372
I highly recommend you create a bootable macOS USB installer so you have more options in case something goes wrong. You can just run the installer from within macOS as well, but if you don't have access to another compatible Mac having a USB installer is a good thing to have ready if something goes wrong.
Make sure to have a good backup before attempting to upgrade macOS.
Upgrading from El Capitan 10.11.6
