VBA Script That Will Update The Desired Range With Numbers

I want to make a VBA script that will update the desired range with numbers like so, i have a table:

columns = A - G
rows = 2 - 5

1st case:
if in one of the cells is entered the value 17 the next cell will be 15.
2nd case:
if in one of the cells is entered the value 15 the next cell to be blank.

and from here just loop until the hole table is filled in with the numbers.
basically all the table should look like:
| 17 | 15 | empty | 17 | 15 | empty | .... and so on.

To be honest I've search the forums, google, I've documented myself in some ways, and even tried to make this "program"... I kinda got it right, but with a button, I wanna do it "live" right after entering the value in the cell and hitting enter the table to update. I understood that "Workseet_Change()" is like a (live screen update).