Minecraft version change is not possible?

I have not been able to change my Minecraft version since the last time and there's a server to the right of the bar. I clicked on it to download it but it still does not work or I do not know where to put the server.jar file in which folder. I have already trying to reinstall my Minecraft.

The Server.jar is if you want to open a server in your localhost.

Uninstall Minecraft and install it again maybe it works.

I have often reinstalled my minecraft it still does not work

Then please ask the Mojang support.