Dear Yigit,
thank you ver much for your response and help!

First I added
define(‘WP_MEMORY_LIMIT’, ’256M’); in the main directory but without success.

To control the php memory I installed the plugin WP-Memory-Usage and indeed memory limit was still at 128 MB.

Then I added php.ini in the main directory with
memory_limit=256M

and finally I got 256MB memeory limit:

PHP Version : 5.3.29 / 32Bit OS
Memory limit : 256 MB
Memory usage : 20.35 MB

After that changes installation of enfold.zip has been successful.

Thanks for your immediate help.
Michael