Update Quantity

I have a records list (approx 1300+ items) in sheet1 with columns
ItemCode - A
Item - B
Type - C
Qty - D
Price - E

The Qty column has number which actually is in kilos
For eg 500.000 means 500.000kg.
What is required is
in sheet2
in column A will be ItemCode and B will be Qty
I mention ItemCode and the respective Qty booked .ie
for eg
ItemCode Qty
111A 5
109V 2
111A 0.250
1234F 1
109V 0.750
111A 2

It matches the ItemCode in Sheet1 and deducts the mentioned
quantity from the Qty column. As in above eg 111A booked is
8.000 , 109V is 2.750 , 1234F is 1. This will get deducted from
the list is Sheet1.

thanks