SFTP Errors when upgrading from 4.4.2 to 4.5.3

Hi all,

For a while I have not made updates to my WP blog and it currently stands at Version 4.4.2. Today, I want to follow the suggestion and upgrade to version 4.5.3. For the first time during an upgrade procedure, WP asks for my FTP credentials.

Question: is that normal? And why does this happen for 4.5.3 the first time?

Now, I checked my hosting provider to ensure I got the hostname and username and password right, but the WP upgrade dialog says the user/pass combination is wrong. In parallel, I have installed WinSCP, and there the combination user/pass works. The only two things I can think of is a) that my blog resides in a subdirectory /blog/wp and b) that my hosting provider uses virtual hosts, so the hostname provided does not match the domain name of the blog.

Question: could someone point to please to a solution to this issue, or explain what is wrong and what I need to do?

Many thanks.