Beim Upload von Bildern kommt die Fehlermeldung HTTP-Error
AddHandler php5-cgi .php

increase upload size

it is commonly known, that the php.ini has values for that:

post_max_size = 256M
upload_max_filesize = 256M
max_execution_time = 300

Note, that if you have configured your wordpress to be a network-installation you will also have to check your admin-panel under My Sites-> Network Admin-> Settings-> Max upload file size.