For some unknown reason my forum can't update anymore. After step 1 'confirm update' , the screen stays white and I can't reach step 2, 'log in'. Just a white screen with a header. I tried all different browsers, none of them seems to be working. We have serious safety-issues by now. How can I update the forum??

Please upload a fresh set of files from your client area, then run the upgrade from /admin/upgrade. This should resolve the issue for you