That a crazy thing. I lost my some data. If you upgrade the system, you need to backup all data first. Best thing is give MAMP folder to MAMP_old and then Install MAMP. After that, just copy htdocs and db folder to MAMP. After you can change the default port. Mysql may not work. So, try this
$lsof -i | grep mysql
mysqld 11714 saturngod 10u IPv4 0x0c108a8c 0t0 TCP *:mysql (LISTEN)
you will see PID number and kill it.
$ kill -9 11714
Restart MAMP again.