How to connect to server via cyberduck FTP client after changing websites url for "http" to "https"

Need more information to truly answer, but a couple of notes that may help you:

If you're explicitly specifying a port, make sure you're using the right one:

• non-encrypted web traffic (HTTP) normally connects on port 80,
• encrypted web-traffic (HTTPS) normally connects on port 443,
• non-encrypted FTP normally connects on port 20,
• encrypted FTPS normally connects on port 21 or 990/989 (and alot of firewalls/NAT traditionally have issues with it),
• encrypted SFTP is totally different from FTPS: SFTP is SSH (port 22),
• ^ some servers don't use either of these ports, but in your circumstances this is unlikely

Are you connecting with the domain name, or with the IP address?

• depending on your server backend (ubuntu, centos, debian, apache, nginx, etc etc etc) domains may be handled differently between HTTP/S and redirects might cause odd functionality
• unless you know what you're doing (e.g. more advanced user, dealing with load balancers, elasticity, etc), best practice is to always connect via the IP address of your server - this will a) connect faster because your DNS doesn't have to look up the IP which it uses anyways, b) helps remove any chance of a weird server configuration or domain redirects affecting you, and c) is just generally more secure and dependable than relying on a domain name.

The above is highly generalized advice - without knowing deeper details (which may not be safe to distribute in a public forum), there's not a lot else I can offer info-wise. Depending on your hosting provider, they may also be able to offer you some advice (either via knowledgebase articles, how-to's, or support). I also haven't ever used CyberDuck so can't offer any advice or recommendations specific to the application, either.

Good luck