If you already know the pixel density of your screen please move on to the next stage, for all others:

Right click your Windows Desktop and click 'Display Settings'





















Make sure you select the correct monitor you wish to see the resolution for. Once done, scroll down until you see the heading 'Screen Resolution' and note down the two numbers (in my case, 2560 and 1440)

Open File Explorer (Windows shortcut is WIN + E) and in the address bar type %appdata% and then press enter















Once you are in the AppData folder, scroll down and open the 'Frontier' folder (Don't mistake it for the Frontier Developments folder if it exists!)





















Once inside the folder, open the RCT3 folder and make a copy of the file options.txt (just in case you need to rollback your changes in the case of a problem).

Once a copy has been made of options.txt, open the original file and on the top line change the two numbers following 'Resolution' to the numbers acquired in Part 1 of this guide.











Save and close the file.

The process is complete, launch the game and have fun!

Hopefully Frontier will address this and patch in more screen resolutions so this manual process is not required.