This really depends on the editor you are using, which you don't mention. In JOSM you can copy the tags of any object to a new one, one (Ctrl+Shift+V), in other editors it may not be possible. I currently don't know of any editor that allows you to "expand" a node in to a way, so typically you will draw a new polygon/area and copy the tags to that, worst case one by one.

This really depends on the editor you are using, which you don't mention. In JOSM you can copy the tags of any object to a new one, in other editors it may not be possible. I currently don't know of any editor that allows you to "expand" a node in to a way, so typically you will draw a new polygon/area and copy the tags to that, worst case one by one.