I opted to use FTP for upgrading Magento as I lack the technical skills to navigate SSH.
Initially, I came across the 500 internal server error, followed by the blank page Google Checkout error. After resolving those, I am now dealing with a missing stylesheet problem.
Upon inspection of the bare page, it seems that Magento is operating on version 1.8.1, but both the frontend and backend lack stylesheets. When checking the link in the view source, the css path leads to a 404 error.
<link rel="stylesheet" type="text/css" href="http://www.mydomainname.com/media/css/aa5d6dfa090eec7ba8c2982f89737fca.css" />
If you have any insight on how to resolve this issue, please share. Thank you!