Before you can get the information, you need to decide what it is exactly that you wish to change.
Generally it will be the amount of money you have when you load up a previously saved game, but it could be (depending on the game) what your current score is, how much energy the character in the game has, or perhaps what level you start on.
(To keep this simple I will assume that you want to change the amount of money you have in a save game. )
If you have already got a save game, run the game and load it, otherwise
load the game and begin a new game, then save it.
Once you have loaded the game, pause it, (if possible) to stop any changes occurring.
Now find the figure that you want to change, (in this case the current balance of money in the game) and write it down. eg. 1000 credits/dollars/pounds/gold etc.
At this point re-save the game, I will tell you why in a second.
Now exit the game to dos (or whatever operating system it is that you use)
Now if you are using dos, while in the directory of the game, type DIR /OD this will give you a directory listing, sorted with the most recent file being shown last. Assuming you keep your computers clock up to date, the most recent file should be the one I told you to re-save above.
If the most recent file does not have todays date, type DATE to see what your computer thinks is the date, and look for any files with this date,
If the date shown is correct then check any sub directories using DIR /OD /S /A /P this will display all files in this directory and all sub directories, including all hidden files and pause at every screen full. Keep an eye on every file's date and time, until you see any with todays date and a recent time.
Write down the file name you find, and the directory that it is stored in.
By now you should have something like this written down:
Now you have acquired the necessary information to hack the save game
file you loaded!