If you name the input fields like this using a character say - that you know will not occur in your item names:
<input name="Shoes-1" size=2>
<input name="Shoes-2" size=2>
<input name="Shoes-3" size=2>
<input name="Shoes-4" size=2>
<input name="Shoes-5" size=2>
and likewise Tires etc. then it will be easy for you to
test whether the form has sent you back "Shoes-2" etc. and if it has, you can use a SQL Update statement to modify just the one column in one row:
update ... set qty2 = ... where name = "Shoes";