Upgrade MySQL to 5.7

First, go to https://dev.mysql.com/downloads/repo/apt/ and click “Download” button, on next page, copy the link that says “No thanks, just start my download.”, it should point to something like https://dev.mysql.com/get/mysql-apt-config_0.7.3-1_all.deb

Use the link to wget the file. then

    sudo dpkg -i mysql-apt-config_0.7.3-1_all.deb

Select 5.7 during configuration.

Remove the previous version of MySQL:

    sudo apt-get remove mysql-client-5.5 mysql-server-5.5  # or 5.6
    sudo apt-get autoremove

Install MySQL 5.7

    sudo apt-get update
    sudo apt-get install mysql-server-5.7

Upgrade databases

    sudo mysql_upgrade -u root -p --force