The recent Linux Mint 21 release has been getting some good press – if you want to join in the fun by upgrading, here’s how.
You can upgrade to Linux Mint 21 from Linux Mint 20.3. If you use a much older version of Linux Mint you will likely need to upgrade to 20.3 before you can skip on ahead to the latest version.
To upgrade to Linux Mint 21 you need an active internet connection, at least 3GB free disk space, and a bit of patience.
Upgrading to Linux Mint 21
Step 1: Install Mint Upgrade

This tool is required to perform the a Linux Mint upgrade. Install this tool by searching for “Mint Upgrade” in the Software Manager app, or run sudo apt install mintupgrade
in a new Terminal window.
Step 2: Run Mint Upgrade

Open a new Terminal window and run sudo mintupgrade check
to check for the latest release. Enter your password when prompted. An upgrade assistant window will open. Click “Let’s Go” in the upgrade assistant window to continue.
Mint Upgrade will run a series tests to make sure you can upgrade safely. By default the tool will advise you to create a backup using Timeshift, as in this window:

If you do not want to make a backup (or you cannot make a backup due to insufficient free space) click the hamburger icon in the window title bar, select Preferences, and, in the ‘Requirements’ section, slide the toggle for ‘Recent Timeshift snapshot’ to the off position:

Click the back arrow in the window title (not the ‘x’) to return to the main upgrade screen. Click “Check again” to proceed.
When all tests are successfully passed the Mint Upgrade tool will tell you about ‘Phase 2’. Click “Ok” to continue.

Step 4: Review proposed changes

An overview of packages to be upgraded, downloaded, installed, and, where needed, removed will be presented to you. Pay attention to download size and space needed. Once you’re happy to proceed with hit ‘OK’.
Step 5: Start the upgrade

Click the “OK” button on the phase 3 dialog to begin upgrading Linux Mint 20.3 to 21.
The Mint Upgrade tool will download all required packages, unpack them, and then install them.

This process will take some time. You can continue to use your computer during this time but you may experience some minor performance issues.
Step 6: Clean orphan packages

Towards the end of the upgrade process you may see a scary-looking notice about orphan packages.
Orphan packages are ones you’ve (likely) installed from a PPA or another third-party repo. It also applies to apps, tools, and libraries available in the previous Linux Mint repo but no longer included in the new ones.
Select (by clicking) all of the packages you want to keep. Packages you don’t select will be removed when you click ‘Fix’.
Step 7: Reboot to finish!

Reboot your computer when prompted to by the upgrade assistant. Once your system comes back up you can proceed to login with your usual account credentials.
Enjoy exploring your Linux Mint 21 upgrade!