After install redmine 3.2, you may import the data of old version redmine to redmine 3.2.
1) Create a new clean database
sudo mysql -u root -p drop database redmine;CREATE DATABASE redmine character SET utf8; GRANT ALL privileges ON redmine.* TO 'redmine'@'localhost';
2) Import old redmine database to new redmine
/usr/bin/mysql -u root -p redmine < /redmine_db_dir/redmine_db_16_02_27.sql
3) Generate new secret and Update db and plugins
sudo su - redmine cd redmine rake generate_secret_token rake db:migrate RAILS_ENV=production rake redmine:plugins:migrate RAILS_ENV=production rake tmp:cache:clear rake tmp:sessions:clear exit