Excel 2002 retain formula in cells while deleting or changing numbers

I have set up some fairly simple worksheets to track business expenses, etc in Excel 2002. Theyre working wonderfully but I want to know how to change the numbers in a particular cell without changing/deleting the formula – basically how to keep the formula intact while entering a different number. For example, in one column I have the amount a vendor charged me for something – the running subtotals are all working properly but suppose that after I review the worksheet I find that I entered the wrong amount the vendor charged and thus need to change the amount. If I simply delete the incorrect amount and type in the new amount does it alter the original formula that’s keeping track of my subtotals?