I installed an usbwebserver (version 8.7) and a mediawiki on an USB- stick.
When I start usbwebserver it works fine and tells me php Version 5.4.17 is installed.
If I start mediawiki I get the error "required php- Version is at least 5.5.9.
How can I install a newer php on the stick?
I do not know, what information you need to answer my question. It is installed as a windows Version.
Download the Windows release of PHP 5.6 from the official site, open the archive and overwrite all matching files on the USB stick with files from the zip. If the folder structure doesn't match, you're probably better off keeping the existing structure on the USB stick since the LAMP setup might be dependent on those specific paths.