How do I create a macro including if statement & automatically

I need to create a worksheet where I can have a list of various data and if
I change the value of one row and that is of a higher value than any other in
this list , I need this row to jump to the top of the worksheet.

This should then happen automatically, ie every time you enter a sum in the
value column it should perform the if statetment automatically and check
wether the top value cell has got a higher value than the sum I just typed in.

Anyone got any ideas of how to do this?