Still can't log into my admin panel

I updated to 4.0 when it was released and subsequently had problems logging into the admin panel. I didn’t connect the problem to the update at the time so I contacted my hosting company (Hostgator) for assistance. They tried a number of fixes with the end result of having to restore my site to a previous version, which meant I had to redo some of the changes I had made. Today I backed up and updated again and I am having the same problem. I read through some of the posts but I am still not clear what I am supposed to do. Should I manually upload the update file into my FTP or just certain sections?

My website is https://serendology.com

Thank you!