If you downloaded 2020 from Steam, you already have it. If you have a CD version not connected to Steam, you may want to see about using it to get the Steam version and get the 64-bit version. WARNING! Not all items work in 64-bit. For instance, the Gas Turbine that comes with Sherman Hill, the first scenario is like a video guide to the loco, and it derails immediately in 64-bit while it runs fine in 32-bit; I'm told this applies to many official scenarios that are older. So for older routes, I still recommend running in 32-bit. Go to 64-bit for the more snazzy and newer/updated stuff.
Go in to your Railworks folder and you will see RailWorks64.exe It does not matter if the game was bought on a disk as it will have installed on your computer. Peter
It should also ask you if you'd like to run 64 bit if you launch from within Steam. If it doesn't, the suggestion to run the 64 bit from the shortcut in your Railworks folder will do it.