List based on criteria if criteria changes list locks

Ok so i'm pretty simple when it comes to excel but for some reason I've been tasked with creating a costing spreadsheet that will eventually spit out the cost of developing a course by the data entered.

I've got the basic shape of it, but have come across an issue I have the following flow:

No of Units= Manually entered no say between 1-10
based on the number entered above it then give you the associated number of headers U1-U10 in below cells =IF(G4>=1,N1,"") G4 is the manually entered number and N1 = U1-U10 populates from a list at side.
Underneath each of these is then a drop down with selection = small/medium/large this is only displays as an option if the cell above has a U1-U10 header in.
This works fine so if you select 10, 10 cells appear under with U1-U10 in underneath 10 drop downs appear and if I select small to medium in each it then generates the number of pages in that unit and then totals up for me to calculate how many pages in the product.
However if I've selected all the drop downs to something then want to change the initial input from 10 to say 5 the headers disappear and give me blank boxes like I wanted but the drop downs underneath remain stuck on the previous selection so therefore it leaves a number of pages in the chain under this and I cannot figure out how to reset the drop down?

Any help much appreciated.
Thanks

I've attached the spreadsheet, its the G4 cell that feeds the initial flow. Many Thanks