Ok, I have a sheet which holds all my stock items with the amount. And on a seperate sheet a simple form.
I will try to explain the problem with an example.

On the form it will have (sheet 1)
ID:10002
Amount: 7
>button with macro asgined<

On sheet 2, where stock levels are stored.
ID:10002
Amount: 13

I need the form to lookup the ID number the user has enterd, then find it in sheet 2 and change the amount of that entry. So 13+7.

Any help would be much appreciated.