Update Data From Database Using Combobox?

Im now creating an inventory system for my project.

i having difficulty with my project im using combobox to select data from database and i want to update the data. if i selected second row of the data it will update the first row of the data.

eg.
"comboboxitem_name" - red ball pen
- blue ball pen
- black ball pen
"quantitytextbox"- 100
"reorder_quantitytextbox"-20

when i selected the "blue ball pen" and fill the information that i want to update then press the submit button. the red ball pen will update with the information that i want to update to "blue ball pen" and the "red ball pen" will change it name to

"blue ball pen". and now i have two "blue ball pen", one with "red ball pen" information and the other one with original "blue ball pen" information.