All the versions of Calibre can be found here at
https://calibre-ebook.com/download
You can download the version of your choice from there (the official calibre download site).
The latest version is v5.11 and the list of changes can be seen at
https://calibre-ebook.com/whats-new
If you are having a specific problem, can you please tell us all the steps you have taken to get the problem. Then some one should be able to try and work out the problem.
I am not seeing an issue downloading a Windows 10 msi from the website