The Linux Mint team has opened up an upgrade path for Mint 19.3 users to jump to Mint 20. Upgrading does come with risks compared to a clean install so be sure to follow the instructions carefully.
Ulyana RSS
The Linux Mint project has tested and approved the Linux Mint 20 ISO images and third-party mirrors have begun hosting the ISOs in anticipation of the final announcement from the Mint team.
The Linux Mint team has started pushing Linux Mint 20 beta images to third-party mirrors. The new update comes with several updates to packages like LibreOffice and the Linux kernel.
The Linux Mint 20 beta ISO images are currently being tested for public consumption. Once released, the public can give last-minute feedback before the official ISOs are made available.
Linux Mint 20 has been codenamed Ulyana. All subsequent releases in the 20.x series will also likely start with the letter 'U'. The project also reiterated that it will drop 32-bit ISO support.