The updating process with most Mac software is painless, especially App Store apps. Not so with MAMP. Since I have such a hard time remembering the process, here’s quick reference to update MAMP Pro without losing databases and local site settings:
Browse to Applications folder and rename the MAMP directory to MAMP_OLD
Unzip the MAMP installer and run the install
Go to the MAMP_OLD directory, copy the db and htdocs directories, and paste into the new MAMP folder. Overwrite what is there.
This update process works for me without any port errors. If you have connection errors, double check the Apache and MySQL ports in the General tab of MAMP. I personally use 80, 443, and 3306 rather than the default.