Where are 2.9.1 upgrade errors displayed on server?

Hi … I have tried several times to upgrade from 2.9 to 2.91 using the “automatic upgrade” feature. I have used this feature 2 or 3 times before and it has worked flawlessly. I backed-up all my blog files using FTP from the server to my desktop. I have de-activated all my plug-ins but when I click on the “automatic upgrade” button, I see ..
– Unpacking the update
– Verifying the unpacked files
– Installing the latest version
and then it seems to “stall” with no icons indicating that any actions are taking place. When I check my blog the “maintenance” message is displayed but after 5 minutes, my blog display returns but the “automatic update” screen remains unchanged.

Is there a folder I can examine on the server that will display errors or tell me why the automatic upgrade is failing?

As well, can you please recommend a tutorial to help me FTP future upgrades to avoid this automatic upgrade that appears to no longer work for me.

Thanks in advance for any support.