similar problem.
I tried to update from moodle 3.2.3 moodle 3.3.2 (zip-file)
When I try to access moodle in the browser to start the update-process then there is only a white page.
I split this from the original post as it really isn't a similar problem at all.
How far do you get before you get a 'white page'. Check the end of your web server's error log. Anything?