I have a small install on CentOS 6. I saw the message in the web interface about the php version, so I tried updating it from 5.3.3 to 5.6. I got a blank page after that. I found the tip about editing php.ini to set memory_limit = 1024M but that didn't work. I removed 5.6 and went back to 5.3.3 and made the php.ini edit again, but no luck. (Full system restart after each change)