I have a macbook pro, late 2013, (910.9.5), Retina. How do I upgrade to Catalina

How to upgrade to macOS Catalina. Catalina will not run 32-bit apps, so you need to delete them or upgrade them to 64-bit apps. See Go64 to find and remove 32-bit apps.

Before You Upgrade macOS

1. Fix any problems before upgrading.
2. Run First Aid in Disk Utility while booted from your Recovery HD.
3. Backup. Make a bootable clone using CarbonCopy Cloner or use TimeMachine.
4. Be sure your startup disk has 18-20GB of free space during the installation.
5. Upgrade third-party software for compatibility. See App Compatibility Table - RoaringApps. If you have mission critical software, then DO NOT upgrade until you know that software is compatible with the version of macOS you are about to install.
6. Disconnect all third-party peripherals.
7. Download the installer which will be in the Applications folder. Quit the installer after it opens, then make a copy of the installer and save it in the Downloads folder. The one in the Applications folder will be deleted after a successful installation.
8. The download is large, anywhere between 5 and 9GBs. It takes time to complete. Be patient.
9. Double-click on the installer in the Applications folder. Click on the start button to begin the installation.

Hi.

System Preferences > Software update and select install Catalina, though you'd better take backup data before install Catalina.

Also should notice that Catalina doesn't support 32bit apps, so if you still need to use 32bit apps, you should stay Mojave.