The official page for Redmine upgrade is here. Below I will write down the instructions I use when upgrading to the latest version of Redmine.
Note that I have cloned Mercurial (Hg) repository and am updating by pulling the latest changes.
So, here goes.
rake db:migrate RAILS_ENV=productionbundle installbundle updaterake redmine:plugins:migrate RAILS_ENV=productionrake tmp:cache:clearrake tmp:sessions:clearThat's it!