I have retried to upgrade, following exactly the stepts in the guidelines. The same result! I have downgraded once again. I got to writing the following line into my browser’s address field:
https://www.maha-online.de/blog/wp-admin/upgrade.php
It produced a white page. Then I typed in:
https://www.maha-online.de/blog/wp-admin/
and got another white page while the address line changed to:
https://www.maha-online.de/blog/wp-admin/upgrade.php?_wp_http_referer=%2Fblog%2Fwp-admin%2F
(Just one line)
What does that mean? Please, give me at least a hint where I can look for a solution. I never had any problems with upgrading so far, and I did not deviate from the instructions, so there must be something wrong here.