Same steps as usual? Just edit the php version?
Unfortunately, that won't work for PHP 5.6 betas as they are downloaded from a separate dev download url from official PHP 5.3/5.4/5.5 versions. I'm waiting for PHP 5.6 GA stable release first which should be using same download url format as current PHP versions. At which then changing PHP version and/or specifying version in menu option #5 for php upgrade should work (provided no bugs)
some benchmarks PHP 5.6 benchmarks http://www.lornajane.net/posts/2014/php-5-6-benchmarks Wordpress 3.9 + PHP 5.4 vs 5.6 vs 5.7 http://ckon.wordpress.com/2014/05/31/php-5-4-vs-5-6-wordpress-3-9-benchmark/ http://ckon.wordpress.com/2014/05/30/php-5-6-enters-final-beta-faster-performance/
When will be 5.7 be released? http://ckon.wordpress.com/2014/05/31/php-5-4-vs-5-6-wordpress-3-9-benchmark/
not yet as 5.7 is in alpha and doesn't fully support all PHP extensions yet https://wiki.php.net/phpng