How to upgrade MYSQL from 5.6.12 to 5.6.21?
First take a backup of everything using your normal backup software.

Take a dump (mysqldump using the --all-databases) option.

Export:

mysqldump -uroot -p --all-databases &gt; alldb.sql
mysqldump -uroot -p --opt --all-databases &gt; alldb.sql
mysqldump -uroot -p --all-databases --skip-lock-tables &gt; alldb.sql


I cordially invite you to look at the docco for the options that suit
you best - or just run mysqldump with the --help option only.

Uninstall your MySQL 5.6.12. (I'm assuming yum or apt - redhat or Ubuntu - again
check your docco)

Install your MySQL 5.6.21.

Check the release notes to ensure that there are no parameters
that have changed - given that your migrating between minor 
versions, this should not be an issue.

Perform a restore using mysql and the dump.

Import:

mysql -u root -p &lt; alldb.sql


Et voilà!