Build Agent Downgrade

Hi,

I know that when a build agent that has been connected to a TC server with a lower version gets connected to a new TC server with higher version, the build agent upgrades automatically. But what if the build agent was connected to a higher version TC server and now gets connected to a TC server with a lower version? 

Does the build agent get downgraded automatically and it happens seamlessly? If not, can we downgrade the server manually?