I downloaded an old version of Forge then put a mod on it, it wasn't compatible so I deleted Forge from 'versions' and downloaded a new one.
When I opened the Minecraft launcher again, it only showed the old deleted Forge, and when I try to open it, it says
The version you are trying to play inherits properties of an unknown version
How do I completely remove this old version of Forge so that Minecraft will recognise the new one?