How to update a plugin

My Plugin page shows several plugins that say in Red : NEEDS UPGRADE and some say: CAN UPGRADE
When I click on the plugin, I see no direct way to do this - such “push this button to upgrade”! which would have been so nice.

So what is the procedure for upgrading a plugin I am using.?
Do I have to redo the whole thing. Delete the plugin and then download a new one and then reconnect it to the code?
Thanks for instructing me how this should be done.

When you click on the plugin, on the right side, check for a dropdown called “currently installed version”