Upgrade symfony 2.3 LTS to 2.6 - symfony

Question

I would like upgrade my symfony app which is based on symfony 2.3. I want to use the new feature with the bootstrap theme for forms.
I never make an symfony upgrade before so I read this chapter from symfony cookbook.
http://symfony.com/doc/current/cookbook/upgrading.html
After that, I have made changes in my "composer.json" and type "composer update symfony/symfony", but I get the following error messages
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- don't install symfony/event-dispatcher 2.6.x-dev|don't install symfony/symfony v2.6.3
- don't install symfony/symfony v2.6.3|remove symfony/event-dispatcher 2.6.x-dev
- Installation request for symfony/symfony 2.6.3 -> satisfiable by symfony/symfony[v2.6.3].
- Installation request for symfony/event-dispatcher == 2.6.9999999.9999999-dev -> satisfiable by symfony/event-dispatcher[2.6.x-dev].
My "composer.json":
{
"name": "symfony/framework-standard-edition",
"license": "MIT",
"type": "project",
"description": "The \"Symfony Standard Edition\" distribution",
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
"symfony/symfony": "2.6.*",
"doctrine/orm": "~2.2,>=2.2.3",
"doctrine/doctrine-bundle": "1.2.*",
"twig/extensions": "1.0.*",
"symfony/assetic-bundle": "2.3.*",
"kriswallsmith/assetic": "1.1.2",
"symfony/swiftmailer-bundle": "2.3.*",
"symfony/monolog-bundle": "2.4.*",
"sensio/distribution-bundle": "2.3.*",
"sensio/framework-extra-bundle": "2.3.*",
"sensio/generator-bundle": "2.3.*",
"incenteev/composer-parameter-handler": "~2.0",
"knplabs/knp-menu": "2.0.*#dev",
"knplabs/knp-menu-bundle": "2.0.*#dev",
"symfony/event-dispatcher": "2.6.*#dev",
"knplabs/doctrine-behaviors": "dev-master",
"a2lix/translation-form-bundle": "dev-master",
"knplabs/knp-paginator-bundle": "~2.4",
"jms/serializer-bundle": "~0.13"
},
"scripts": {
"post-install-cmd": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
],
"post-update-cmd": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
]
},
"config": {
"bin-dir": "bin"
},
"minimum-stability": "stable",
"extra": {
"symfony-app-dir": "app",
"symfony-web-dir": "web",
"incenteev-parameters": {
"file": "app/config/parameters.yml"
},
"branch-alias": {
"dev-master": "2.3-dev"
}
}
}
Can someone give me a tip?

Answer 1

You shouldn't have to manually specify the event dispatcher at all. Remove that, then take a look at this file:
https://github.com/symfony/symfony-standard/blob/2.6/composer.json
Make sure your composer dependencies match everything. Also make sure you have "dev-master": "2.6-dev" under branch-alias