This tutorial helps you update your OP installation to the newest version.
It is based on CentOS and an MySQL database

1. Upgrade to 3.0.14

First I updated to v3.0.14 with the correct plugins (v3.0.14) and Ruby 2.1.2.
Change the version of the plugins in the Gemfile.plugins file to ‘v3.0.14’

Stop the httpd service and the delayed_job

service httpd stop
su - openproject -c "bash -l"
cd ~/openproject
RAILS_ENV="production" bundle exec script/delayed_job start

*Set OP version to v3.0 and upgrade Ruby
Change the version of the plugins in the Gemfile.plugins file to ‘v3.0.14’*

git checkout release/3.0
git reset --hard
git pull

rvm install 2.1.2
rvm use --default 2.1.2
gem install bundler
bundle install

bundle exec rake db:migrate
bundle exec rake generate_secret_token     
RAILS_ENV="production" bundle exec rake db:migrate
RAILS_ENV="production" bundle exec rake db:seed
RAILS_ENV="production" bundle exec rake assets:precompile

gem install passenger
passenger-install-apache2-module

copy paste the output in the httpd.conf file

2. Upgrade to 4.0:

su - openproject -c "bash -l"
rvm install 2.1.4
rvm use --default 2.1.4

*Change plugins version to stable
removed the openproject-plugins line in Gemfile.plugins*

git reset --hard
git checkout stable
git pull
bundle install

*got an error about sprockets-2.2.2.backport2
used:* - This is fixed in 4.0.1

wget https://aws-eu-cache01.rubygems.org/gems/sprockets-2.2.2.backport2.gem
gem install sprockets-2.2.2.backport2.gem

bundle install

Then i installed python

exit
yum install python python-pip
pip install nodeenv
su - openproject -c "bash -l" 
cd ~/openproject
nodeenv nodeenv
source ./nodeenv/bin/activate
npm -g install bower
npm install
bower install

Migrate the DB

bundle exec rake db:migrate
bundle exec rake generate_secret_token     
RAILS_ENV="production" bundle exec rake db:migrate
RAILS_ENV="production" bundle exec rake db:seed
RAILS_ENV="production" bundle exec rake assets:precompile

*Install passenger and apache.
And copy the output in httpd.conf*

su - openproject -c "bash -l" 
cd ~/openproject
gem install passenger
passenger-install-apache2-module

Start Apache

service httpd start

Start the delayed job

su - openproject -c "bash -l" 
cd ~/openproject
RAILS_ENV="production" bundle exec script/delayed_job start

and you’re done ;-)

Now i tried updating directly to Ruby 2.1.4 but after the update i couldn’t change the work package status.
So this worked for me.

Updated 25-11-2014