combobox

Question

i have combobox that have  numbers from 1 to 7
when i select any number automatically  the program create comboboxes depends on the number selected from the first combox that have the number from 1 to 7
now , when i select number 2 there is two comboboxes created  , when i select after that number 3 there is another one is created and added , 

the problem is when i choose number less than the first selected i mean if i choose number 3 and i want to choose again number 1 the comboboxes is not deleted or hidden, they still created 

how can i do that when i increase the number of decrease the comboboxes also have the same changing