If you're running Linux Mint 19.3 and you'd like to UPGRADE to Linux Mint 20, typically to take advantage of new software and increased system capabilities that Mint 20 brings to the table, begin by reading the following upgrade advice and instructions from Linux Mint:

1: https://blog.linuxmint.com/

2: https://community.linuxmint.com/tutorial/view/2485

Once you've read Clem's upgrade advice and you've gone through the UPGRADE tutorial section by section, if you're up to what this procedure requires then set aside some time and do exactly what the tutorial outlines step by step.

I did it. It works perfectly as long as you don't lose track of where you are or miss an important step - as I did the first time I went through it. I failed to run "sudo apt autoremove" at the end of the initial test run section of the tutorial to get rid of unnecessary and conflicting packages the system had identified and advised me to remove.

I created an up to date 'system snapshot' with Timeshift before starting the upgrade, so when that first attempt went south I simply rebooted then reinstalled that latest system snapshot using Timeshift - and Mint 19.3 was returned to where it originally was once again.

Next time around I didn't forget to run "sudo apt autoremove" at the end of the initial test run section to rid the system of unnecessary and conflicting packages. From there through the end of the upgrade things worked perfectly.

Once the upgrade was done the next step (prior to rebooting) was to open the Software Sources app, click the 'Maintenance' tab, select the 'Downgrade Foreign Packages' section, click 'Select All' and downgrade those packages so they continue to work in Mint 20.

Then reboot and the upgrade is done.

Everything you have installed in Mint 19.3 will be available to you in Mint 20. A package or two may need updating, for example Wine needed to be updated to 4.12 via the Mint Update utility before it worked flawlessly. But that was handled automatically so nothing to worry about.

Took a little over an hour to complete the full upgrade and it's working without problems of any sort. Still exploring everything that's new with Mint 20, but that's the fun part!..

The voyage of discovery that truly matters is not in seeking new lands but in seeing with new eyes.