How can I manage that when I switching from Production to Local Host and in reverse all the changes will apply? How do I import changes from, when the site was live to when I switch it to the localhost. Is there a simple way to do so, without downloading databases and switching them?
The short answer is — no, there is no simple way.
WP is designed to work within a boundries of a single database as installed and with core exclusively manipulating that data. There are no concepts of database being manipulated partially and externally.
The most common and reliable workflow is that you copy database from production to development, but never in other direction. This is (relatively) easy to implement and production is safe from being wrecked.
If you do need to do complete or partial updates to production things get a lot more complicated and error–prone. There are some dedicated products out there, such as RAMP, but generally I had never heard anyone consider it anything but huge unsolved headache.