Why are the changes, I upload to webserver, not visible in the web browser?

There is probably some caching taking place on the web server, in your web browser, or somewhere in between.

Most web browsers have command that clears its own cache and requests the web server to clear its cache before reloading the page. Usually the command can be invoked using Ctrl+F5 keyboard shortcut.

If the above does not help or if you believe the server should pick up the change automatically, make sure the timestamp of uploaded file has proper value, so that the web server can recognize the file has changed.

Read more about timestamps to find out, how to configure timestamp conversion properly. Also make sure you understand, why the true remote timestamp may actually be different to the local one.1

As a last resort solution you may try to disable Preserve timestamp transfer setting to let remote server to keep the upload time as the last modification time of the file.