There are two ways to remove an item your basket. The easiest way is simply to click on the basket icon on the top-right of the screen:
Then click on the bin/trash icon on the right-hand side.
From here, you can go to your full basket page by clicking on the basket icon, bottom-left.
You can remove an item from your basket from this page by clicking the X.
To change the quantity in your basket, click on the Qty drop-down to change the quantity followed by the Update Basket link