First check with the website that your computer is fully qualifying for the minimum specs. If you are working on projects currently be warned they may not load correctly or save. The new version still has some bugs.
Be warned it will replace your current version.
If you are OK with that open MEP 2021 and click on Help. Go to Update on line. The box mat appear underneath the program, check for it in the task bar. It should show if there are any updates to be had.