Welcome to the forums, tlittle10ny.
There are quite a few recent threads on the T:ANE forum that will show you the steps to take to easily and safely accomplish the task of transferring your Trainz program and Userdata files to another Hard Disk Drive.
Here's one current example:
https://forums.auran.com/trainz/sho...E-with-all-of-it-s-content-to-my-second-drive
My recommendation is to COPY your current T:ANE files and folders to the larger drive and to set it up so that it is functioning properly and to your satisfaction before blowing away the existing T:ANE files on your C: drive.
The good news is that with most Trainz versions, you don't need to worry about System Registry settings, so copying and pasting works a treat - and is the best way to back up your installation to boot.
Keeping it simple also helps:
Suggest creating a TANE folder on your largest, fastest drive with sufficient space - say D:\TANE.
Then create a subdirectory called 'Userdata' (or similar) inside your D:\TANE folder. (Thus; D:\TANE\Userdata - or similar).
Locate and COPY all of your current user data folders and files into the new Userdata sub-directory on D: (or wherever).
In a similar fashion, COPY all of the existing T:ANE program files and folders to the new folder at D:\TANE.
Follow the instructions in the linked post above to get the executable to work as a startup shortcut, and complete the Trainz Settings dialog parameters to suit your needs and log-in authentication settings, etc. in the T:ANE Launcher to get things running smoothly once again.