composer php - symfony upgrade from 2.3 to 2.7 -

i'm trying upgrade symfony 2.3 2.7 using recomendations in knp blog composer gave me this:

loading composer repositories package information updating dependencies (including require-dev) requirements not resolved installable set of packages.    problem 1     - conclusion: don't install symfony/symfony v2.7.1     - don't install symfony/symfony v2.7.0|remove symfony/var-dumper v2.6.7     - don't install symfony/var-dumper v2.6.7|don't install symfony/symfony v2.7.0     - don't install symfony/symfony v2.7.0|don't install symfony/var-dumper v2.6.7     - installation request symfony/symfony 2.7.* -> satisfiable symfony/symfony[v2.7.0, v2.7.1].     - installation request symfony/var-dumper == 2.6.7.0 -> satisfiable symfony/var-dumper[v2.6.7]. 

i try change composer.json to:

{   "name": "symfony/framework-standard-edition",   "license": "mit",   "type": "project",   "autoload": {     "psr-4": {       "": "src/",       "symfonystandard\\": "app/symfonystandard/"     }   },   "require": {     "php": ">=5.3.9",     "symfony/symfony": "2.7.*",     "doctrine/orm": "~2.2,>=2.2.3,<2.5",     "doctrine/dbal": "<2.5",     "doctrine/doctrine-bundle": "~1.4",     "symfony/assetic-bundle": "~2.3",     "symfony/swiftmailer-bundle": "~2.3",     "symfony/monolog-bundle": "~2.4",     "sensio/distribution-bundle": "~4.0",     "sensio/framework-extra-bundle": "~3.0,>=3.0.2",     "incenteev/composer-parameter-handler": "~2.0"   },   "require-dev": {     "sensio/generator-bundle": "~2.3"   },   "scripts": {     "post-root-package-install": [       "symfonystandard\\composer::hookrootpackageinstall"     ],     "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",       "sensio\\bundle\\distributionbundle\\composer\\scripthandler::removesymfonystandardfiles",       "sensio\\bundle\\distributionbundle\\composer\\scripthandler::preparedeploymenttarget"     ],     "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",       "sensio\\bundle\\distributionbundle\\composer\\scripthandler::removesymfonystandardfiles",       "sensio\\bundle\\distributionbundle\\composer\\scripthandler::preparedeploymenttarget"     ]   },   "config": {     "bin-dir": "bin"   },   "extra": {     "symfony-app-dir": "app",     "symfony-web-dir": "web",     "symfony-assets-install": "relative",     "incenteev-parameters": {       "file": "app/config/parameters.yml"     }   } } 

which copy of fresh instalation symfony 2.7 composer.json "composer" returns same error.

i'm not finding what's wrong. can me?

thanks in advance!!

try launch update process corresponding dependencies:

composer update symfony/symfony sensio/distribution-bundle --with-dependencies 

you can try update single packages with:

composer update symfony/symfony twig/twig sensio/distribution-bundle