Winhack
To perform hex editing you will need a program like Winhack or Codex.
The interface of Winhack isn’t that complex. The two panels show the same section of the game’s memory in a 16 x 16 grid. The left panel shows each byte as a 2 digit hexadecimal number and the right shows the ASCII representation of the same bytes.
Most editing will be done with the hexadecimal numbers, but the ASCII representation is useful for finding and/or editing strings used by the save game. The numbers along the side and top of each grid are the address of the bytes.
At the top of Winhack’s window you can chose the process you want to edit, this will be RCT.EXE or RCT2.EXE. In the bottom of the window you have a search function to search for a particular string in the game’s memory.
Each object in the game map is represented by 8 bytes. So each row in the grid is two objects. Note that objects starting with FF have been deleted.
In the screen shot of Winhack you can see that the same 8 bytes are repeated, this is because they are all identical objects, grass land tiles.