2. Convert that number into hex with a calculator. Eg. 12129
3. Add a 0 to the beginning if it's an odd number of digits. Eg 012129
4. Think of the number in pairs. Eg. 01 21 29
5. Reverse the order of the pairs. Eg 29 21 01
6. Add the gz extension to the savestate.
7. Unzip the savestate with 7-z.
8. Open the uncompressed savestate with a hex editor and search for the number sequence from step 5 (no spaces).
9. Change the value replacing the string with FFFFFFF or whatever you want to change the value too (keep in mind you have to reverse the order of the pairs if you have a specific number you want to change it to).
10. Save and recompress the uncompressed file with 7-zip.
11. Delete the gz extension.
12. Load the game and see if it worked. If it didn't reset the changed code to its original value, find where the number occurs again in the savestate: recompress, reload, repeat.