Typically you change integer values which are stored as hex in the save file. You can search for money or lives and change the hex to be a different number. Start with something easy like money which is a specific number (1 life will appear a lot in hex). Google 'float to hex' and change money from something like 32,000 to 33,000.
Some editors like HxD have good search options. Set code to little endian if it asks, all hex is stored backwards. So if you need to write 33,000 it's saved on the gamesaves as 008e0074 (hex reads correctly 4700e800). Or maybe it's 00e80047, dunno