This is the item screen. It shows you all the particulars relating to that item. Scroll down until you see the Price and Inventory section. (below)
Click on the blue text that shows Stock [-2 In Stock]. This will bring up the Adjust Stock panel.
Now select the reason for adjusting the stock. If you have just received a shipment of this item from the supplier, you should always use Stock Received as you are adding to the stock levels.
Enter the amount of new stock. Then click the blue save button.
NOTE: If you find that the stock levels are NEGATIVE or INACCURATE, then you should do a stock take on that item. Count every single item of this product including what you have just received PLUS what is already on the shelves, then use the Inventory Re-count option. Here you type in the total amount of that item.
Back at the Price and Inventory screen, you will see that the blue text showing the stock has increased by the amount you entered. in this case we added +1, changing it from -2 to -1.
Press the blue save button.
If you have other items to adjust, repeat the same steps above.